diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index ab2cc1f3b8519..1629717ff2861 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -13594,10 +13594,10 @@ namespace ts {
                 // }
                 //
                 // The implied type of the first clause number | string.
-                // The implied type of the second clause is string (but this doesn't get used).
+                // The implied type of the second clause is never, but this does not get just because it includes a default case.
                 // The implied type of the third clause is boolean (number has already be caught).
                 if (!(hasDefaultClause || (type.flags & TypeFlags.Union))) {
-                    let impliedType = getTypeWithFacts(getUnionType(clauseWitnesses.map(text => typeofTypesByName.get(text) || neverType)), switchFacts);
+                    let impliedType = getTypeWithFacts(getUnionType((<string[]>clauseWitnesses).map(text => typeofTypesByName.get(text) || neverType)), switchFacts);
                     if (impliedType.flags & TypeFlags.Union) {
                         impliedType = getAssignmentReducedType(impliedType as UnionType, getBaseConstraintOfType(type) || type);
                     }
@@ -19027,17 +19027,20 @@ namespace ts {
             if (hasDefault) {
                 // Value is not equal to any types after the active clause.
                 for (let i = end; i < witnesses.length; i++) {
-                    facts |= typeofNEFacts.get(witnesses[i]) || TypeFacts.TypeofNEHostObject;
+                    const witness = witnesses[i];
+                    facts |= (witness && typeofNEFacts.get(witness)) || TypeFacts.TypeofNEHostObject;
                 }
                 // Remove inequalities for types that appear in the
                 // active clause because they appear before other
                 // types collected so far.
                 for (let i = start; i < end; i++) {
-                    facts &= ~(typeofNEFacts.get(witnesses[i]) || 0);
+                    const witness = witnesses[i];
+                    facts &= ~((witness && typeofNEFacts.get(witness)) || 0);
                 }
                 // Add inequalities for types before the active clause unconditionally.
                 for (let i = 0; i < start; i++) {
-                    facts |= typeofNEFacts.get(witnesses[i]) || TypeFacts.TypeofNEHostObject;
+                    const witness = witnesses[i];
+                    facts |= (witness && typeofNEFacts.get(witness)) || TypeFacts.TypeofNEHostObject;
                 }
             }
             // When in an active clause without default the set of
@@ -19045,12 +19048,14 @@ namespace ts {
             else {
                 // Add equalities for all types in the active clause.
                 for (let i = start; i < end; i++) {
-                    facts |= typeofEQFacts.get(witnesses[i]) || TypeFacts.TypeofEQHostObject;
+                    const witness = witnesses[i];
+                    facts |= (witness && typeofEQFacts.get(witness)) || TypeFacts.TypeofEQHostObject;
                 }
                 // Remove equalities for types that appear before the
                 // active clause.
                 for (let i = 0; i < start; i++) {
-                    facts &= ~(typeofEQFacts.get(witnesses[i]) || 0);
+                    const witness = witnesses[i];
+                    facts &= ~((witness && typeofEQFacts.get(witness)) || 0);
                 }
             }
             return facts;
diff --git a/tests/baselines/reference/narrowingByTypeofInSwitch.js b/tests/baselines/reference/narrowingByTypeofInSwitch.js
index 2cf4b9027c2c8..95ec120a85d2d 100644
--- a/tests/baselines/reference/narrowingByTypeofInSwitch.js
+++ b/tests/baselines/reference/narrowingByTypeofInSwitch.js
@@ -35,6 +35,14 @@ function assertAll(x: Basic) {
     return x;
 }
 
+function assertStringOrNumber(x: string | number)  {
+    return x;
+}
+
+function assertBooleanOrObject(x: boolean | object)  {
+    return x;
+}
+
 type Basic = number | boolean | string | symbol | object | Function | undefined;
 
 function testUnion(x: Basic) {
@@ -186,6 +194,22 @@ function switchOrderingWithDefault(x: string | number | boolean) {
         case 'number': return assertNever(x);
     }
 }
+
+function fallThroughTest(x: string | number | boolean | object) {
+    switch (typeof x) {
+        case 'number':
+            assertNumber(x)
+        case 'string':
+            assertStringOrNumber(x)
+            break;
+        default:
+            assertObject(x);
+        case 'number':
+        case 'boolean':
+            assertBooleanOrObject(x);
+            break;
+    }
+}
 
 
 //// [narrowingByTypeofInSwitch.js]
@@ -216,6 +240,12 @@ function assertUndefined(x) {
 function assertAll(x) {
     return x;
 }
+function assertStringOrNumber(x) {
+    return x;
+}
+function assertBooleanOrObject(x) {
+    return x;
+}
 function testUnion(x) {
     switch (typeof x) {
         case 'number':
@@ -425,3 +455,18 @@ function switchOrderingWithDefault(x) {
         case 'number': return assertNever(x);
     }
 }
+function fallThroughTest(x) {
+    switch (typeof x) {
+        case 'number':
+            assertNumber(x);
+        case 'string':
+            assertStringOrNumber(x);
+            break;
+        default:
+            assertObject(x);
+        case 'number':
+        case 'boolean':
+            assertBooleanOrObject(x);
+            break;
+    }
+}
diff --git a/tests/baselines/reference/narrowingByTypeofInSwitch.symbols b/tests/baselines/reference/narrowingByTypeofInSwitch.symbols
index 2d1bd06baba98..b451b39ac7c22 100644
--- a/tests/baselines/reference/narrowingByTypeofInSwitch.symbols
+++ b/tests/baselines/reference/narrowingByTypeofInSwitch.symbols
@@ -67,476 +67,525 @@ function assertUndefined(x: undefined) {
 function assertAll(x: Basic) {
 >assertAll : Symbol(assertAll, Decl(narrowingByTypeofInSwitch.ts, 30, 1))
 >x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 32, 19))
->Basic : Symbol(Basic, Decl(narrowingByTypeofInSwitch.ts, 34, 1))
+>Basic : Symbol(Basic, Decl(narrowingByTypeofInSwitch.ts, 42, 1))
 
     return x;
 >x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 32, 19))
 }
 
+function assertStringOrNumber(x: string | number)  {
+>assertStringOrNumber : Symbol(assertStringOrNumber, Decl(narrowingByTypeofInSwitch.ts, 34, 1))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 36, 30))
+
+    return x;
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 36, 30))
+}
+
+function assertBooleanOrObject(x: boolean | object)  {
+>assertBooleanOrObject : Symbol(assertBooleanOrObject, Decl(narrowingByTypeofInSwitch.ts, 38, 1))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 40, 31))
+
+    return x;
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 40, 31))
+}
+
 type Basic = number | boolean | string | symbol | object | Function | undefined;
->Basic : Symbol(Basic, Decl(narrowingByTypeofInSwitch.ts, 34, 1))
+>Basic : Symbol(Basic, Decl(narrowingByTypeofInSwitch.ts, 42, 1))
 >Function : Symbol(Function, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
 
 function testUnion(x: Basic) {
->testUnion : Symbol(testUnion, Decl(narrowingByTypeofInSwitch.ts, 36, 80))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 38, 19))
->Basic : Symbol(Basic, Decl(narrowingByTypeofInSwitch.ts, 34, 1))
+>testUnion : Symbol(testUnion, Decl(narrowingByTypeofInSwitch.ts, 44, 80))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 46, 19))
+>Basic : Symbol(Basic, Decl(narrowingByTypeofInSwitch.ts, 42, 1))
 
     switch (typeof x) {
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 38, 19))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 46, 19))
 
         case 'number': assertNumber(x); return;
 >assertNumber : Symbol(assertNumber, Decl(narrowingByTypeofInSwitch.ts, 2, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 38, 19))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 46, 19))
 
         case 'boolean': assertBoolean(x); return;
 >assertBoolean : Symbol(assertBoolean, Decl(narrowingByTypeofInSwitch.ts, 6, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 38, 19))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 46, 19))
 
         case 'function': assertFunction(x); return;
 >assertFunction : Symbol(assertFunction, Decl(narrowingByTypeofInSwitch.ts, 18, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 38, 19))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 46, 19))
 
         case 'symbol': assertSymbol(x); return;
 >assertSymbol : Symbol(assertSymbol, Decl(narrowingByTypeofInSwitch.ts, 14, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 38, 19))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 46, 19))
 
         case 'object': assertObject(x); return;
 >assertObject : Symbol(assertObject, Decl(narrowingByTypeofInSwitch.ts, 22, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 38, 19))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 46, 19))
 
         case 'string': assertString(x); return;
 >assertString : Symbol(assertString, Decl(narrowingByTypeofInSwitch.ts, 10, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 38, 19))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 46, 19))
 
         case 'undefined': assertUndefined(x); return;
 >assertUndefined : Symbol(assertUndefined, Decl(narrowingByTypeofInSwitch.ts, 26, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 38, 19))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 46, 19))
     }
     assertNever(x);
 >assertNever : Symbol(assertNever, Decl(narrowingByTypeofInSwitch.ts, 0, 0))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 38, 19))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 46, 19))
 }
 
 function testExtendsUnion<T extends Basic>(x: T) {
->testExtendsUnion : Symbol(testExtendsUnion, Decl(narrowingByTypeofInSwitch.ts, 49, 1))
->T : Symbol(T, Decl(narrowingByTypeofInSwitch.ts, 51, 26))
->Basic : Symbol(Basic, Decl(narrowingByTypeofInSwitch.ts, 34, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 51, 43))
->T : Symbol(T, Decl(narrowingByTypeofInSwitch.ts, 51, 26))
+>testExtendsUnion : Symbol(testExtendsUnion, Decl(narrowingByTypeofInSwitch.ts, 57, 1))
+>T : Symbol(T, Decl(narrowingByTypeofInSwitch.ts, 59, 26))
+>Basic : Symbol(Basic, Decl(narrowingByTypeofInSwitch.ts, 42, 1))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 59, 43))
+>T : Symbol(T, Decl(narrowingByTypeofInSwitch.ts, 59, 26))
 
     switch (typeof x) {
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 51, 43))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 59, 43))
 
         case 'number': assertNumber(x); return;
 >assertNumber : Symbol(assertNumber, Decl(narrowingByTypeofInSwitch.ts, 2, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 51, 43))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 59, 43))
 
         case 'boolean': assertBoolean(x); return;
 >assertBoolean : Symbol(assertBoolean, Decl(narrowingByTypeofInSwitch.ts, 6, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 51, 43))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 59, 43))
 
         case 'function': assertAll(x); return;
 >assertAll : Symbol(assertAll, Decl(narrowingByTypeofInSwitch.ts, 30, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 51, 43))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 59, 43))
 
         case 'symbol': assertSymbol(x); return;
 >assertSymbol : Symbol(assertSymbol, Decl(narrowingByTypeofInSwitch.ts, 14, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 51, 43))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 59, 43))
 
         case 'object': assertAll(x); return;
 >assertAll : Symbol(assertAll, Decl(narrowingByTypeofInSwitch.ts, 30, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 51, 43))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 59, 43))
 
         case 'string': assertString(x); return;
 >assertString : Symbol(assertString, Decl(narrowingByTypeofInSwitch.ts, 10, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 51, 43))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 59, 43))
 
         case 'undefined': assertUndefined(x); return;
 >assertUndefined : Symbol(assertUndefined, Decl(narrowingByTypeofInSwitch.ts, 26, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 51, 43))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 59, 43))
     }
     assertAll(x);
 >assertAll : Symbol(assertAll, Decl(narrowingByTypeofInSwitch.ts, 30, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 51, 43))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 59, 43))
 }
 
 function testAny(x: any) {
->testAny : Symbol(testAny, Decl(narrowingByTypeofInSwitch.ts, 62, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 64, 17))
+>testAny : Symbol(testAny, Decl(narrowingByTypeofInSwitch.ts, 70, 1))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 72, 17))
 
     switch (typeof x) {
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 64, 17))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 72, 17))
 
         case 'number': assertNumber(x); return;
 >assertNumber : Symbol(assertNumber, Decl(narrowingByTypeofInSwitch.ts, 2, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 64, 17))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 72, 17))
 
         case 'boolean': assertBoolean(x); return;
 >assertBoolean : Symbol(assertBoolean, Decl(narrowingByTypeofInSwitch.ts, 6, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 64, 17))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 72, 17))
 
         case 'function': assertFunction(x); return;
 >assertFunction : Symbol(assertFunction, Decl(narrowingByTypeofInSwitch.ts, 18, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 64, 17))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 72, 17))
 
         case 'symbol': assertSymbol(x); return;
 >assertSymbol : Symbol(assertSymbol, Decl(narrowingByTypeofInSwitch.ts, 14, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 64, 17))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 72, 17))
 
         case 'object': assertObject(x); return;
 >assertObject : Symbol(assertObject, Decl(narrowingByTypeofInSwitch.ts, 22, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 64, 17))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 72, 17))
 
         case 'string': assertString(x); return;
 >assertString : Symbol(assertString, Decl(narrowingByTypeofInSwitch.ts, 10, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 64, 17))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 72, 17))
 
         case 'undefined': assertUndefined(x); return;
 >assertUndefined : Symbol(assertUndefined, Decl(narrowingByTypeofInSwitch.ts, 26, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 64, 17))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 72, 17))
     }
     assertAll(x); // is any
 >assertAll : Symbol(assertAll, Decl(narrowingByTypeofInSwitch.ts, 30, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 64, 17))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 72, 17))
 }
 
 function a1(x: string | object | undefined) {
->a1 : Symbol(a1, Decl(narrowingByTypeofInSwitch.ts, 75, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 77, 12))
+>a1 : Symbol(a1, Decl(narrowingByTypeofInSwitch.ts, 83, 1))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 85, 12))
 
     return x;
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 77, 12))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 85, 12))
 }
 
 function testUnionExplicitDefault(x: Basic) {
->testUnionExplicitDefault : Symbol(testUnionExplicitDefault, Decl(narrowingByTypeofInSwitch.ts, 79, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 81, 34))
->Basic : Symbol(Basic, Decl(narrowingByTypeofInSwitch.ts, 34, 1))
+>testUnionExplicitDefault : Symbol(testUnionExplicitDefault, Decl(narrowingByTypeofInSwitch.ts, 87, 1))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 89, 34))
+>Basic : Symbol(Basic, Decl(narrowingByTypeofInSwitch.ts, 42, 1))
 
     switch (typeof x) {
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 81, 34))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 89, 34))
 
         case 'number': assertNumber(x); return;
 >assertNumber : Symbol(assertNumber, Decl(narrowingByTypeofInSwitch.ts, 2, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 81, 34))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 89, 34))
 
         case 'boolean': assertBoolean(x); return;
 >assertBoolean : Symbol(assertBoolean, Decl(narrowingByTypeofInSwitch.ts, 6, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 81, 34))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 89, 34))
 
         case 'function': assertFunction(x); return;
 >assertFunction : Symbol(assertFunction, Decl(narrowingByTypeofInSwitch.ts, 18, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 81, 34))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 89, 34))
 
         case 'symbol': assertSymbol(x); return;
 >assertSymbol : Symbol(assertSymbol, Decl(narrowingByTypeofInSwitch.ts, 14, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 81, 34))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 89, 34))
 
         default: a1(x); return;
->a1 : Symbol(a1, Decl(narrowingByTypeofInSwitch.ts, 75, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 81, 34))
+>a1 : Symbol(a1, Decl(narrowingByTypeofInSwitch.ts, 83, 1))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 89, 34))
     }
 }
 
 function testUnionImplicitDefault(x: Basic) {
->testUnionImplicitDefault : Symbol(testUnionImplicitDefault, Decl(narrowingByTypeofInSwitch.ts, 89, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 91, 34))
->Basic : Symbol(Basic, Decl(narrowingByTypeofInSwitch.ts, 34, 1))
+>testUnionImplicitDefault : Symbol(testUnionImplicitDefault, Decl(narrowingByTypeofInSwitch.ts, 97, 1))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 99, 34))
+>Basic : Symbol(Basic, Decl(narrowingByTypeofInSwitch.ts, 42, 1))
 
     switch (typeof x) {
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 91, 34))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 99, 34))
 
         case 'number': assertNumber(x); return;
 >assertNumber : Symbol(assertNumber, Decl(narrowingByTypeofInSwitch.ts, 2, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 91, 34))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 99, 34))
 
         case 'boolean': assertBoolean(x); return;
 >assertBoolean : Symbol(assertBoolean, Decl(narrowingByTypeofInSwitch.ts, 6, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 91, 34))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 99, 34))
 
         case 'function': assertFunction(x); return;
 >assertFunction : Symbol(assertFunction, Decl(narrowingByTypeofInSwitch.ts, 18, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 91, 34))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 99, 34))
 
         case 'symbol': assertSymbol(x); return;
 >assertSymbol : Symbol(assertSymbol, Decl(narrowingByTypeofInSwitch.ts, 14, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 91, 34))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 99, 34))
     }
     return a1(x);
->a1 : Symbol(a1, Decl(narrowingByTypeofInSwitch.ts, 75, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 91, 34))
+>a1 : Symbol(a1, Decl(narrowingByTypeofInSwitch.ts, 83, 1))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 99, 34))
 }
 
 function testExtendsExplicitDefault<T extends Basic>(x: T) {
->testExtendsExplicitDefault : Symbol(testExtendsExplicitDefault, Decl(narrowingByTypeofInSwitch.ts, 99, 1))
->T : Symbol(T, Decl(narrowingByTypeofInSwitch.ts, 101, 36))
->Basic : Symbol(Basic, Decl(narrowingByTypeofInSwitch.ts, 34, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 101, 53))
->T : Symbol(T, Decl(narrowingByTypeofInSwitch.ts, 101, 36))
+>testExtendsExplicitDefault : Symbol(testExtendsExplicitDefault, Decl(narrowingByTypeofInSwitch.ts, 107, 1))
+>T : Symbol(T, Decl(narrowingByTypeofInSwitch.ts, 109, 36))
+>Basic : Symbol(Basic, Decl(narrowingByTypeofInSwitch.ts, 42, 1))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 109, 53))
+>T : Symbol(T, Decl(narrowingByTypeofInSwitch.ts, 109, 36))
 
     switch (typeof x) {
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 101, 53))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 109, 53))
 
         case 'number': assertNumber(x); return;
 >assertNumber : Symbol(assertNumber, Decl(narrowingByTypeofInSwitch.ts, 2, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 101, 53))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 109, 53))
 
         case 'boolean': assertBoolean(x); return;
 >assertBoolean : Symbol(assertBoolean, Decl(narrowingByTypeofInSwitch.ts, 6, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 101, 53))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 109, 53))
 
         case 'function': assertAll(x); return;
 >assertAll : Symbol(assertAll, Decl(narrowingByTypeofInSwitch.ts, 30, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 101, 53))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 109, 53))
 
         case 'symbol': assertSymbol(x); return;
 >assertSymbol : Symbol(assertSymbol, Decl(narrowingByTypeofInSwitch.ts, 14, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 101, 53))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 109, 53))
 
         default: assertAll(x); return;
 >assertAll : Symbol(assertAll, Decl(narrowingByTypeofInSwitch.ts, 30, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 101, 53))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 109, 53))
 
     }
 }
 
 function testExtendsImplicitDefault<T extends Basic>(x: T) {
->testExtendsImplicitDefault : Symbol(testExtendsImplicitDefault, Decl(narrowingByTypeofInSwitch.ts, 110, 1))
->T : Symbol(T, Decl(narrowingByTypeofInSwitch.ts, 112, 36))
->Basic : Symbol(Basic, Decl(narrowingByTypeofInSwitch.ts, 34, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 112, 53))
->T : Symbol(T, Decl(narrowingByTypeofInSwitch.ts, 112, 36))
+>testExtendsImplicitDefault : Symbol(testExtendsImplicitDefault, Decl(narrowingByTypeofInSwitch.ts, 118, 1))
+>T : Symbol(T, Decl(narrowingByTypeofInSwitch.ts, 120, 36))
+>Basic : Symbol(Basic, Decl(narrowingByTypeofInSwitch.ts, 42, 1))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 120, 53))
+>T : Symbol(T, Decl(narrowingByTypeofInSwitch.ts, 120, 36))
 
     switch (typeof x) {
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 112, 53))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 120, 53))
 
         case 'number': assertNumber(x); return;
 >assertNumber : Symbol(assertNumber, Decl(narrowingByTypeofInSwitch.ts, 2, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 112, 53))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 120, 53))
 
         case 'boolean': assertBoolean(x); return;
 >assertBoolean : Symbol(assertBoolean, Decl(narrowingByTypeofInSwitch.ts, 6, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 112, 53))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 120, 53))
 
         case 'function': assertAll(x); return;
 >assertAll : Symbol(assertAll, Decl(narrowingByTypeofInSwitch.ts, 30, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 112, 53))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 120, 53))
 
         case 'symbol': assertSymbol(x); return;
 >assertSymbol : Symbol(assertSymbol, Decl(narrowingByTypeofInSwitch.ts, 14, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 112, 53))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 120, 53))
     }
     return assertAll(x);
 >assertAll : Symbol(assertAll, Decl(narrowingByTypeofInSwitch.ts, 30, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 112, 53))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 120, 53))
 }
 
 type L = (x: number) => string;
->L : Symbol(L, Decl(narrowingByTypeofInSwitch.ts, 120, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 122, 10))
+>L : Symbol(L, Decl(narrowingByTypeofInSwitch.ts, 128, 1))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 130, 10))
 
 type R = { x: string, y: number }
->R : Symbol(R, Decl(narrowingByTypeofInSwitch.ts, 122, 31))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 123, 10))
->y : Symbol(y, Decl(narrowingByTypeofInSwitch.ts, 123, 21))
+>R : Symbol(R, Decl(narrowingByTypeofInSwitch.ts, 130, 31))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 131, 10))
+>y : Symbol(y, Decl(narrowingByTypeofInSwitch.ts, 131, 21))
 
 function exhaustiveChecks(x: number | string | L | R): string {
->exhaustiveChecks : Symbol(exhaustiveChecks, Decl(narrowingByTypeofInSwitch.ts, 123, 33))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 125, 26))
->L : Symbol(L, Decl(narrowingByTypeofInSwitch.ts, 120, 1))
->R : Symbol(R, Decl(narrowingByTypeofInSwitch.ts, 122, 31))
+>exhaustiveChecks : Symbol(exhaustiveChecks, Decl(narrowingByTypeofInSwitch.ts, 131, 33))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 133, 26))
+>L : Symbol(L, Decl(narrowingByTypeofInSwitch.ts, 128, 1))
+>R : Symbol(R, Decl(narrowingByTypeofInSwitch.ts, 130, 31))
 
     switch (typeof x) {
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 125, 26))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 133, 26))
 
         case 'number': return x.toString(2);
 >x.toString : Symbol(Number.toString, Decl(lib.d.ts, --, --))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 125, 26))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 133, 26))
 >toString : Symbol(Number.toString, Decl(lib.d.ts, --, --))
 
         case 'string': return x;
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 125, 26))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 133, 26))
 
         case 'function': return x(42);
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 125, 26))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 133, 26))
 
         case 'object': return x.x;
->x.x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 123, 10))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 125, 26))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 123, 10))
+>x.x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 131, 10))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 133, 26))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 131, 10))
     }
 }
 
 function exhaustiveChecksGenerics<T extends L | R | number | string>(x: T): string {
->exhaustiveChecksGenerics : Symbol(exhaustiveChecksGenerics, Decl(narrowingByTypeofInSwitch.ts, 132, 1))
->T : Symbol(T, Decl(narrowingByTypeofInSwitch.ts, 134, 34))
->L : Symbol(L, Decl(narrowingByTypeofInSwitch.ts, 120, 1))
->R : Symbol(R, Decl(narrowingByTypeofInSwitch.ts, 122, 31))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 134, 69))
->T : Symbol(T, Decl(narrowingByTypeofInSwitch.ts, 134, 34))
+>exhaustiveChecksGenerics : Symbol(exhaustiveChecksGenerics, Decl(narrowingByTypeofInSwitch.ts, 140, 1))
+>T : Symbol(T, Decl(narrowingByTypeofInSwitch.ts, 142, 34))
+>L : Symbol(L, Decl(narrowingByTypeofInSwitch.ts, 128, 1))
+>R : Symbol(R, Decl(narrowingByTypeofInSwitch.ts, 130, 31))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 142, 69))
+>T : Symbol(T, Decl(narrowingByTypeofInSwitch.ts, 142, 34))
 
     switch (typeof x) {
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 134, 69))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 142, 69))
 
         case 'number': return x.toString(2);
 >x.toString : Symbol(toString, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --) ... and 2 more)
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 134, 69))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 142, 69))
 >toString : Symbol(toString, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --) ... and 2 more)
 
         case 'string': return x;
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 134, 69))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 142, 69))
 
         case 'function': return (x as L)(42); // Can't narrow generic
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 134, 69))
->L : Symbol(L, Decl(narrowingByTypeofInSwitch.ts, 120, 1))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 142, 69))
+>L : Symbol(L, Decl(narrowingByTypeofInSwitch.ts, 128, 1))
 
         case 'object': return (x as R).x;            // Can't narrow generic
->(x as R).x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 123, 10))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 134, 69))
->R : Symbol(R, Decl(narrowingByTypeofInSwitch.ts, 122, 31))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 123, 10))
+>(x as R).x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 131, 10))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 142, 69))
+>R : Symbol(R, Decl(narrowingByTypeofInSwitch.ts, 130, 31))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 131, 10))
     }
 }
 
 function multipleGeneric<X extends L, Y extends R>(xy: X | Y): [X, string] | [Y, number] {
->multipleGeneric : Symbol(multipleGeneric, Decl(narrowingByTypeofInSwitch.ts, 141, 1))
->X : Symbol(X, Decl(narrowingByTypeofInSwitch.ts, 143, 25))
->L : Symbol(L, Decl(narrowingByTypeofInSwitch.ts, 120, 1))
->Y : Symbol(Y, Decl(narrowingByTypeofInSwitch.ts, 143, 37))
->R : Symbol(R, Decl(narrowingByTypeofInSwitch.ts, 122, 31))
->xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 143, 51))
->X : Symbol(X, Decl(narrowingByTypeofInSwitch.ts, 143, 25))
->Y : Symbol(Y, Decl(narrowingByTypeofInSwitch.ts, 143, 37))
->X : Symbol(X, Decl(narrowingByTypeofInSwitch.ts, 143, 25))
->Y : Symbol(Y, Decl(narrowingByTypeofInSwitch.ts, 143, 37))
+>multipleGeneric : Symbol(multipleGeneric, Decl(narrowingByTypeofInSwitch.ts, 149, 1))
+>X : Symbol(X, Decl(narrowingByTypeofInSwitch.ts, 151, 25))
+>L : Symbol(L, Decl(narrowingByTypeofInSwitch.ts, 128, 1))
+>Y : Symbol(Y, Decl(narrowingByTypeofInSwitch.ts, 151, 37))
+>R : Symbol(R, Decl(narrowingByTypeofInSwitch.ts, 130, 31))
+>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 151, 51))
+>X : Symbol(X, Decl(narrowingByTypeofInSwitch.ts, 151, 25))
+>Y : Symbol(Y, Decl(narrowingByTypeofInSwitch.ts, 151, 37))
+>X : Symbol(X, Decl(narrowingByTypeofInSwitch.ts, 151, 25))
+>Y : Symbol(Y, Decl(narrowingByTypeofInSwitch.ts, 151, 37))
 
     switch (typeof xy) {
->xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 143, 51))
+>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 151, 51))
 
         case 'function': return [xy, xy(42)];
->xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 143, 51))
->xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 143, 51))
+>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 151, 51))
+>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 151, 51))
 
         case 'object': return [xy, xy.y];
->xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 143, 51))
->xy.y : Symbol(y, Decl(narrowingByTypeofInSwitch.ts, 123, 21))
->xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 143, 51))
->y : Symbol(y, Decl(narrowingByTypeofInSwitch.ts, 123, 21))
+>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 151, 51))
+>xy.y : Symbol(y, Decl(narrowingByTypeofInSwitch.ts, 131, 21))
+>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 151, 51))
+>y : Symbol(y, Decl(narrowingByTypeofInSwitch.ts, 131, 21))
 
         default: return assertNever(xy);
 >assertNever : Symbol(assertNever, Decl(narrowingByTypeofInSwitch.ts, 0, 0))
->xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 143, 51))
+>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 151, 51))
     }
 }
 
 function multipleGenericFuse<X extends L | number, Y extends R | number>(xy: X | Y): [X, number] | [Y, string] | [(X | Y)] {
->multipleGenericFuse : Symbol(multipleGenericFuse, Decl(narrowingByTypeofInSwitch.ts, 149, 1))
->X : Symbol(X, Decl(narrowingByTypeofInSwitch.ts, 151, 29))
->L : Symbol(L, Decl(narrowingByTypeofInSwitch.ts, 120, 1))
->Y : Symbol(Y, Decl(narrowingByTypeofInSwitch.ts, 151, 50))
->R : Symbol(R, Decl(narrowingByTypeofInSwitch.ts, 122, 31))
->xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 151, 73))
->X : Symbol(X, Decl(narrowingByTypeofInSwitch.ts, 151, 29))
->Y : Symbol(Y, Decl(narrowingByTypeofInSwitch.ts, 151, 50))
->X : Symbol(X, Decl(narrowingByTypeofInSwitch.ts, 151, 29))
->Y : Symbol(Y, Decl(narrowingByTypeofInSwitch.ts, 151, 50))
->X : Symbol(X, Decl(narrowingByTypeofInSwitch.ts, 151, 29))
->Y : Symbol(Y, Decl(narrowingByTypeofInSwitch.ts, 151, 50))
+>multipleGenericFuse : Symbol(multipleGenericFuse, Decl(narrowingByTypeofInSwitch.ts, 157, 1))
+>X : Symbol(X, Decl(narrowingByTypeofInSwitch.ts, 159, 29))
+>L : Symbol(L, Decl(narrowingByTypeofInSwitch.ts, 128, 1))
+>Y : Symbol(Y, Decl(narrowingByTypeofInSwitch.ts, 159, 50))
+>R : Symbol(R, Decl(narrowingByTypeofInSwitch.ts, 130, 31))
+>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 159, 73))
+>X : Symbol(X, Decl(narrowingByTypeofInSwitch.ts, 159, 29))
+>Y : Symbol(Y, Decl(narrowingByTypeofInSwitch.ts, 159, 50))
+>X : Symbol(X, Decl(narrowingByTypeofInSwitch.ts, 159, 29))
+>Y : Symbol(Y, Decl(narrowingByTypeofInSwitch.ts, 159, 50))
+>X : Symbol(X, Decl(narrowingByTypeofInSwitch.ts, 159, 29))
+>Y : Symbol(Y, Decl(narrowingByTypeofInSwitch.ts, 159, 50))
 
     switch (typeof xy) {
->xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 151, 73))
+>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 159, 73))
 
         case 'function': return [xy, 1];
->xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 151, 73))
+>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 159, 73))
 
         case 'object': return [xy, 'two'];
->xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 151, 73))
+>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 159, 73))
 
         case 'number': return [xy]
->xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 151, 73))
+>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 159, 73))
     }
 }
 
 function multipleGenericExhaustive<X extends L, Y extends R>(xy: X | Y): [X, string] | [Y, number] {
->multipleGenericExhaustive : Symbol(multipleGenericExhaustive, Decl(narrowingByTypeofInSwitch.ts, 157, 1))
->X : Symbol(X, Decl(narrowingByTypeofInSwitch.ts, 159, 35))
->L : Symbol(L, Decl(narrowingByTypeofInSwitch.ts, 120, 1))
->Y : Symbol(Y, Decl(narrowingByTypeofInSwitch.ts, 159, 47))
->R : Symbol(R, Decl(narrowingByTypeofInSwitch.ts, 122, 31))
->xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 159, 61))
->X : Symbol(X, Decl(narrowingByTypeofInSwitch.ts, 159, 35))
->Y : Symbol(Y, Decl(narrowingByTypeofInSwitch.ts, 159, 47))
->X : Symbol(X, Decl(narrowingByTypeofInSwitch.ts, 159, 35))
->Y : Symbol(Y, Decl(narrowingByTypeofInSwitch.ts, 159, 47))
+>multipleGenericExhaustive : Symbol(multipleGenericExhaustive, Decl(narrowingByTypeofInSwitch.ts, 165, 1))
+>X : Symbol(X, Decl(narrowingByTypeofInSwitch.ts, 167, 35))
+>L : Symbol(L, Decl(narrowingByTypeofInSwitch.ts, 128, 1))
+>Y : Symbol(Y, Decl(narrowingByTypeofInSwitch.ts, 167, 47))
+>R : Symbol(R, Decl(narrowingByTypeofInSwitch.ts, 130, 31))
+>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 167, 61))
+>X : Symbol(X, Decl(narrowingByTypeofInSwitch.ts, 167, 35))
+>Y : Symbol(Y, Decl(narrowingByTypeofInSwitch.ts, 167, 47))
+>X : Symbol(X, Decl(narrowingByTypeofInSwitch.ts, 167, 35))
+>Y : Symbol(Y, Decl(narrowingByTypeofInSwitch.ts, 167, 47))
 
     switch (typeof xy) {
->xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 159, 61))
+>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 167, 61))
 
         case 'object': return [xy, xy.y];
->xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 159, 61))
->xy.y : Symbol(y, Decl(narrowingByTypeofInSwitch.ts, 123, 21))
->xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 159, 61))
->y : Symbol(y, Decl(narrowingByTypeofInSwitch.ts, 123, 21))
+>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 167, 61))
+>xy.y : Symbol(y, Decl(narrowingByTypeofInSwitch.ts, 131, 21))
+>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 167, 61))
+>y : Symbol(y, Decl(narrowingByTypeofInSwitch.ts, 131, 21))
 
         case 'function': return [xy, xy(42)];
->xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 159, 61))
->xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 159, 61))
+>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 167, 61))
+>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 167, 61))
     }
 }
 
 function switchOrdering(x: string | number | boolean) {
->switchOrdering : Symbol(switchOrdering, Decl(narrowingByTypeofInSwitch.ts, 164, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 166, 24))
+>switchOrdering : Symbol(switchOrdering, Decl(narrowingByTypeofInSwitch.ts, 172, 1))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 174, 24))
 
     switch (typeof x) {
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 166, 24))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 174, 24))
 
         case 'string': return assertString(x);
 >assertString : Symbol(assertString, Decl(narrowingByTypeofInSwitch.ts, 10, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 166, 24))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 174, 24))
 
         case 'number': return assertNumber(x);
 >assertNumber : Symbol(assertNumber, Decl(narrowingByTypeofInSwitch.ts, 2, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 166, 24))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 174, 24))
 
         case 'boolean': return assertBoolean(x);
 >assertBoolean : Symbol(assertBoolean, Decl(narrowingByTypeofInSwitch.ts, 6, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 166, 24))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 174, 24))
 
         case 'number': return assertNever(x);
 >assertNever : Symbol(assertNever, Decl(narrowingByTypeofInSwitch.ts, 0, 0))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 166, 24))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 174, 24))
     }
 }
 
 function switchOrderingWithDefault(x: string | number | boolean) {
->switchOrderingWithDefault : Symbol(switchOrderingWithDefault, Decl(narrowingByTypeofInSwitch.ts, 173, 1))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 175, 35))
+>switchOrderingWithDefault : Symbol(switchOrderingWithDefault, Decl(narrowingByTypeofInSwitch.ts, 181, 1))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 183, 35))
 
     function local(y: string | number | boolean) {
->local : Symbol(local, Decl(narrowingByTypeofInSwitch.ts, 175, 66))
->y : Symbol(y, Decl(narrowingByTypeofInSwitch.ts, 176, 19))
+>local : Symbol(local, Decl(narrowingByTypeofInSwitch.ts, 183, 66))
+>y : Symbol(y, Decl(narrowingByTypeofInSwitch.ts, 184, 19))
 
         return x;
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 175, 35))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 183, 35))
     }
     switch (typeof x) {
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 175, 35))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 183, 35))
 
         case 'string':
         case 'number':
         default: return local(x)
->local : Symbol(local, Decl(narrowingByTypeofInSwitch.ts, 175, 66))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 175, 35))
+>local : Symbol(local, Decl(narrowingByTypeofInSwitch.ts, 183, 66))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 183, 35))
 
         case 'string': return assertNever(x);
 >assertNever : Symbol(assertNever, Decl(narrowingByTypeofInSwitch.ts, 0, 0))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 175, 35))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 183, 35))
 
         case 'number': return assertNever(x);
 >assertNever : Symbol(assertNever, Decl(narrowingByTypeofInSwitch.ts, 0, 0))
->x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 175, 35))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 183, 35))
+    }
+}
+
+function fallThroughTest(x: string | number | boolean | object) {
+>fallThroughTest : Symbol(fallThroughTest, Decl(narrowingByTypeofInSwitch.ts, 194, 1))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 196, 25))
+
+    switch (typeof x) {
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 196, 25))
+
+        case 'number':
+            assertNumber(x)
+>assertNumber : Symbol(assertNumber, Decl(narrowingByTypeofInSwitch.ts, 2, 1))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 196, 25))
+
+        case 'string':
+            assertStringOrNumber(x)
+>assertStringOrNumber : Symbol(assertStringOrNumber, Decl(narrowingByTypeofInSwitch.ts, 34, 1))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 196, 25))
+
+            break;
+        default:
+            assertObject(x);
+>assertObject : Symbol(assertObject, Decl(narrowingByTypeofInSwitch.ts, 22, 1))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 196, 25))
+
+        case 'number':
+        case 'boolean':
+            assertBooleanOrObject(x);
+>assertBooleanOrObject : Symbol(assertBooleanOrObject, Decl(narrowingByTypeofInSwitch.ts, 38, 1))
+>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 196, 25))
+
+            break;
     }
 }
 
diff --git a/tests/baselines/reference/narrowingByTypeofInSwitch.types b/tests/baselines/reference/narrowingByTypeofInSwitch.types
index 785bdd23609d5..8672f4c9e7d09 100644
--- a/tests/baselines/reference/narrowingByTypeofInSwitch.types
+++ b/tests/baselines/reference/narrowingByTypeofInSwitch.types
@@ -73,6 +73,22 @@ function assertAll(x: Basic) {
 >x : Basic
 }
 
+function assertStringOrNumber(x: string | number)  {
+>assertStringOrNumber : (x: string | number) => string | number
+>x : string | number
+
+    return x;
+>x : string | number
+}
+
+function assertBooleanOrObject(x: boolean | object)  {
+>assertBooleanOrObject : (x: boolean | object) => boolean | object
+>x : boolean | object
+
+    return x;
+>x : boolean | object
+}
+
 type Basic = number | boolean | string | symbol | object | Function | undefined;
 >Basic : Basic
 >Function : Function
@@ -693,3 +709,49 @@ function switchOrderingWithDefault(x: string | number | boolean) {
     }
 }
 
+function fallThroughTest(x: string | number | boolean | object) {
+>fallThroughTest : (x: string | number | boolean | object) => void
+>x : string | number | boolean | object
+
+    switch (typeof x) {
+>typeof x : "string" | "number" | "boolean" | "symbol" | "undefined" | "object" | "function"
+>x : string | number | boolean | object
+
+        case 'number':
+>'number' : "number"
+
+            assertNumber(x)
+>assertNumber(x) : number
+>assertNumber : (x: number) => number
+>x : number
+
+        case 'string':
+>'string' : "string"
+
+            assertStringOrNumber(x)
+>assertStringOrNumber(x) : string | number
+>assertStringOrNumber : (x: string | number) => string | number
+>x : string | number
+
+            break;
+        default:
+            assertObject(x);
+>assertObject(x) : object
+>assertObject : (x: object) => object
+>x : object
+
+        case 'number':
+>'number' : "number"
+
+        case 'boolean':
+>'boolean' : "boolean"
+
+            assertBooleanOrObject(x);
+>assertBooleanOrObject(x) : boolean | object
+>assertBooleanOrObject : (x: boolean | object) => boolean | object
+>x : boolean | object
+
+            break;
+    }
+}
+
diff --git a/tests/cases/compiler/narrowingByTypeofInSwitch.ts b/tests/cases/compiler/narrowingByTypeofInSwitch.ts
index aadd351b87e00..252c1d9445ac9 100644
--- a/tests/cases/compiler/narrowingByTypeofInSwitch.ts
+++ b/tests/cases/compiler/narrowingByTypeofInSwitch.ts
@@ -37,6 +37,14 @@ function assertAll(x: Basic) {
     return x;
 }
 
+function assertStringOrNumber(x: string | number)  {
+    return x;
+}
+
+function assertBooleanOrObject(x: boolean | object)  {
+    return x;
+}
+
 type Basic = number | boolean | string | symbol | object | Function | undefined;
 
 function testUnion(x: Basic) {
@@ -188,3 +196,19 @@ function switchOrderingWithDefault(x: string | number | boolean) {
         case 'number': return assertNever(x);
     }
 }
+
+function fallThroughTest(x: string | number | boolean | object) {
+    switch (typeof x) {
+        case 'number':
+            assertNumber(x)
+        case 'string':
+            assertStringOrNumber(x)
+            break;
+        default:
+            assertObject(x);
+        case 'number':
+        case 'boolean':
+            assertBooleanOrObject(x);
+            break;
+    }
+}