diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index f279dea186a7a..708b6eaa696f8 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -5621,7 +5621,7 @@ module ts {
             }
 
             var isConstEnum = isConstEnumObjectType(objectType);
-            if (isConstEnum && 
+            if (isConstEnum &&
                 (!node.argumentExpression || node.argumentExpression.kind !== SyntaxKind.StringLiteral)) {
                 error(node.argumentExpression, Diagnostics.A_const_enum_member_can_only_be_accessed_using_a_string_literal);
                 return unknownType;
@@ -5653,10 +5653,10 @@ module ts {
             }
 
             // Check for compatible indexer types.
-            if (indexType.flags & (TypeFlags.Any | TypeFlags.StringLike | TypeFlags.NumberLike) || isTypeAssignableTo(indexType, stringOrNumberType)) {
+            if (isTypeOfKind(indexType, TypeFlags.Any | TypeFlags.StringLike | TypeFlags.NumberLike)) {
 
                 // Try to use a number indexer.
-                if (indexType.flags & (TypeFlags.Any | TypeFlags.NumberLike) || isTypeAssignableTo(indexType, numberType)) {
+                if (isTypeOfKind(indexType, TypeFlags.Any | TypeFlags.NumberLike)) {
                     var numberIndexType = getIndexTypeOfType(objectType, IndexKind.Number);
                     if (numberIndexType) {
                         return numberIndexType;
@@ -6557,7 +6557,7 @@ module ts {
         }
 
         function checkArithmeticOperandType(operand: Node, type: Type, diagnostic: DiagnosticMessage): boolean {
-            if (!(type.flags & (TypeFlags.Any | TypeFlags.NumberLike))) {
+            if (!isTypeOfKind(type, TypeFlags.Any | TypeFlags.NumberLike)) {
                 error(operand, diagnostic);
                 return false;
             }
@@ -6708,12 +6708,21 @@ module ts {
             return numberType;
         }
 
-        // Return true if type an object type, a type parameter, or a union type composed of only those kinds of types
-        function isStructuredType(type: Type): boolean {
+        // Return true if type has the given flags, or is a union type composed of types that all have those flags
+        function isTypeOfKind(type: Type, kind: TypeFlags): boolean {
+            if (type.flags & kind) {
+                return true;
+            }
             if (type.flags & TypeFlags.Union) {
-                return !forEach((<UnionType>type).types, t => !isStructuredType(t));
+                var types = (<UnionType>type).types;
+                for (var i = 0; i < types.length; i++) {
+                    if (!(types[i].flags & kind)) {
+                        return false;
+                    }
+                }
+                return true;
             }
-            return (type.flags & (TypeFlags.ObjectType | TypeFlags.TypeParameter)) !== 0;
+            return false;
         }
 
         function isConstEnumObjectType(type: Type): boolean {
@@ -6730,7 +6739,7 @@ module ts {
             // and the right operand to be of type Any or a subtype of the 'Function' interface type. 
             // The result is always of the Boolean primitive type.
             // NOTE: do not raise error if leftType is unknown as related error was already reported
-            if (!(leftType.flags & TypeFlags.Any || isStructuredType(leftType))) {
+            if (!isTypeOfKind(leftType, TypeFlags.Any | TypeFlags.ObjectType | TypeFlags.TypeParameter)) {
                 error(node.left, Diagnostics.The_left_hand_side_of_an_instanceof_expression_must_be_of_type_any_an_object_type_or_a_type_parameter);
             }
             // NOTE: do not raise error if right is unknown as related error was already reported
@@ -6745,10 +6754,10 @@ module ts {
             // The in operator requires the left operand to be of type Any, the String primitive type, or the Number primitive type,
             // and the right operand to be of type Any, an object type, or a type parameter type.
             // The result is always of the Boolean primitive type.
-            if (leftType !== anyType && leftType !== stringType && leftType !== numberType) {
+            if (!isTypeOfKind(leftType, TypeFlags.Any | TypeFlags.StringLike | TypeFlags.NumberLike)) {
                 error(node.left, Diagnostics.The_left_hand_side_of_an_in_expression_must_be_of_types_any_string_or_number);
             }
-            if (!(rightType.flags & TypeFlags.Any || isStructuredType(rightType))) {
+            if (!isTypeOfKind(rightType, TypeFlags.Any | TypeFlags.ObjectType | TypeFlags.TypeParameter)) {
                 error(node.right, Diagnostics.The_right_hand_side_of_an_in_expression_must_be_of_type_any_an_object_type_or_a_type_parameter);
             }
             return booleanType;
@@ -6909,16 +6918,16 @@ module ts {
                     if (rightType.flags & (TypeFlags.Undefined | TypeFlags.Null)) rightType = leftType;
 
                     var resultType: Type;
-                    if (leftType.flags & TypeFlags.NumberLike && rightType.flags & TypeFlags.NumberLike) {
+                    if (isTypeOfKind(leftType, TypeFlags.NumberLike) && isTypeOfKind(rightType, TypeFlags.NumberLike)) {
                         // Operands of an enum type are treated as having the primitive type Number.
                         // If both operands are of the Number primitive type, the result is of the Number primitive type.
                         resultType = numberType;
                     }
-                    else if (leftType.flags & TypeFlags.StringLike || rightType.flags & TypeFlags.StringLike) {
+                    else if (isTypeOfKind(leftType, TypeFlags.StringLike) || isTypeOfKind(rightType, TypeFlags.StringLike)) {
                         // If one or both operands are of the String primitive type, the result is of the String primitive type.
                         resultType = stringType;
                     }
-                    else if (leftType.flags & TypeFlags.Any || leftType === unknownType || rightType.flags & TypeFlags.Any || rightType === unknownType) {
+                    else if (leftType.flags & TypeFlags.Any || rightType.flags & TypeFlags.Any) {
                         // Otherwise, the result is of type Any.
                         // NOTE: unknown type here denotes error type. Old compiler treated this case as any type so do we.
                         resultType = anyType;
@@ -8274,7 +8283,7 @@ module ts {
             var exprType = checkExpression(node.expression);
             // unknownType is returned i.e. if node.expression is identifier whose name cannot be resolved
             // in this case error about missing name is already reported - do not report extra one
-            if (!(exprType.flags & TypeFlags.Any || isStructuredType(exprType))) {
+            if (!isTypeOfKind(exprType, TypeFlags.Any | TypeFlags.ObjectType | TypeFlags.TypeParameter)) {
                 error(node.expression, Diagnostics.The_right_hand_side_of_a_for_in_statement_must_be_of_type_any_an_object_type_or_a_type_parameter);
             }