diff --git a/src/lib/es2020.bigint.d.ts b/src/lib/es2020.bigint.d.ts
index 05fbbf12ce146..6a126df856661 100644
--- a/src/lib/es2020.bigint.d.ts
+++ b/src/lib/es2020.bigint.d.ts
@@ -223,7 +223,7 @@ interface BigInt64Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike>
     includes(searchElement: bigint, fromIndex?: number): boolean;
 
     /**
-     * Returns the index of the first occurrence of a value in an array.
+     * Returns the index of the first occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
@@ -241,7 +241,7 @@ interface BigInt64Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike>
     keys(): ArrayIterator<number>;
 
     /**
-     * Returns the index of the last occurrence of a value in an array.
+     * Returns the index of the last occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
@@ -500,7 +500,7 @@ interface BigUint64Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike>
     includes(searchElement: bigint, fromIndex?: number): boolean;
 
     /**
-     * Returns the index of the first occurrence of a value in an array.
+     * Returns the index of the first occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
@@ -518,7 +518,7 @@ interface BigUint64Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike>
     keys(): ArrayIterator<number>;
 
     /**
-     * Returns the index of the last occurrence of a value in an array.
+     * Returns the index of the last occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
diff --git a/src/lib/es5.d.ts b/src/lib/es5.d.ts
index ab484e1812e7b..f7581a1c78461 100644
--- a/src/lib/es5.d.ts
+++ b/src/lib/es5.d.ts
@@ -412,14 +412,14 @@ interface String {
     concat(...strings: string[]): string;
 
     /**
-     * Returns the position of the first occurrence of a substring.
+     * Returns the position of the first occurrence of a substring, or -1 if it is not present.
      * @param searchString The substring to search for in the string
      * @param position The index at which to begin searching the String object. If omitted, search starts at the beginning of the string.
      */
     indexOf(searchString: string, position?: number): number;
 
     /**
-     * Returns the last occurrence of a substring in the string.
+     * Returns the last occurrence of a substring in the string, or -1 if it is not present.
      * @param searchString The substring to search for.
      * @param position The index at which to begin searching. If omitted, the search begins at the end of the string.
      */
@@ -1948,7 +1948,7 @@ interface Int8Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
     forEach(callbackfn: (value: number, index: number, array: this) => void, thisArg?: any): void;
 
     /**
-     * Returns the index of the first occurrence of a value in an array.
+     * Returns the index of the first occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      *  search starts at index 0.
@@ -1963,7 +1963,7 @@ interface Int8Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
     join(separator?: string): string;
 
     /**
-     * Returns the index of the last occurrence of a value in an array.
+     * Returns the index of the last occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
@@ -2229,7 +2229,7 @@ interface Uint8Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
     forEach(callbackfn: (value: number, index: number, array: this) => void, thisArg?: any): void;
 
     /**
-     * Returns the index of the first occurrence of a value in an array.
+     * Returns the index of the first occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      *  search starts at index 0.
@@ -2244,7 +2244,7 @@ interface Uint8Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
     join(separator?: string): string;
 
     /**
-     * Returns the index of the last occurrence of a value in an array.
+     * Returns the index of the last occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
@@ -2510,7 +2510,7 @@ interface Uint8ClampedArray<TArrayBuffer extends ArrayBufferLike = ArrayBufferLi
     forEach(callbackfn: (value: number, index: number, array: this) => void, thisArg?: any): void;
 
     /**
-     * Returns the index of the first occurrence of a value in an array.
+     * Returns the index of the first occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      *  search starts at index 0.
@@ -2525,7 +2525,7 @@ interface Uint8ClampedArray<TArrayBuffer extends ArrayBufferLike = ArrayBufferLi
     join(separator?: string): string;
 
     /**
-     * Returns the index of the last occurrence of a value in an array.
+     * Returns the index of the last occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
@@ -2790,7 +2790,7 @@ interface Int16Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
      */
     forEach(callbackfn: (value: number, index: number, array: this) => void, thisArg?: any): void;
     /**
-     * Returns the index of the first occurrence of a value in an array.
+     * Returns the index of the first occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      *  search starts at index 0.
@@ -2805,7 +2805,7 @@ interface Int16Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
     join(separator?: string): string;
 
     /**
-     * Returns the index of the last occurrence of a value in an array.
+     * Returns the index of the last occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
@@ -3071,7 +3071,7 @@ interface Uint16Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
     forEach(callbackfn: (value: number, index: number, array: this) => void, thisArg?: any): void;
 
     /**
-     * Returns the index of the first occurrence of a value in an array.
+     * Returns the index of the first occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      *  search starts at index 0.
@@ -3086,7 +3086,7 @@ interface Uint16Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
     join(separator?: string): string;
 
     /**
-     * Returns the index of the last occurrence of a value in an array.
+     * Returns the index of the last occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
@@ -3351,7 +3351,7 @@ interface Int32Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
     forEach(callbackfn: (value: number, index: number, array: this) => void, thisArg?: any): void;
 
     /**
-     * Returns the index of the first occurrence of a value in an array.
+     * Returns the index of the first occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      *  search starts at index 0.
@@ -3366,7 +3366,7 @@ interface Int32Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
     join(separator?: string): string;
 
     /**
-     * Returns the index of the last occurrence of a value in an array.
+     * Returns the index of the last occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
@@ -3631,7 +3631,7 @@ interface Uint32Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
      */
     forEach(callbackfn: (value: number, index: number, array: this) => void, thisArg?: any): void;
     /**
-     * Returns the index of the first occurrence of a value in an array.
+     * Returns the index of the first occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      *  search starts at index 0.
@@ -3646,7 +3646,7 @@ interface Uint32Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
     join(separator?: string): string;
 
     /**
-     * Returns the index of the last occurrence of a value in an array.
+     * Returns the index of the last occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
@@ -3912,7 +3912,7 @@ interface Float32Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
     forEach(callbackfn: (value: number, index: number, array: this) => void, thisArg?: any): void;
 
     /**
-     * Returns the index of the first occurrence of a value in an array.
+     * Returns the index of the first occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      *  search starts at index 0.
@@ -3927,7 +3927,7 @@ interface Float32Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
     join(separator?: string): string;
 
     /**
-     * Returns the index of the last occurrence of a value in an array.
+     * Returns the index of the last occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
@@ -4193,7 +4193,7 @@ interface Float64Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
     forEach(callbackfn: (value: number, index: number, array: this) => void, thisArg?: any): void;
 
     /**
-     * Returns the index of the first occurrence of a value in an array.
+     * Returns the index of the first occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      *  search starts at index 0.
@@ -4208,7 +4208,7 @@ interface Float64Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike> {
     join(separator?: string): string;
 
     /**
-     * Returns the index of the last occurrence of a value in an array.
+     * Returns the index of the last occurrence of a value in an array, or -1 if it is not present.
      * @param searchElement The value to locate in the array.
      * @param fromIndex The array index at which to begin the search. If fromIndex is omitted, the
      * search starts at index 0.
diff --git a/tests/baselines/reference/1.0lib-noErrors.js b/tests/baselines/reference/1.0lib-noErrors.js
index b190ac91b1594..fc49f788730ec 100644
--- a/tests/baselines/reference/1.0lib-noErrors.js
+++ b/tests/baselines/reference/1.0lib-noErrors.js
@@ -297,14 +297,14 @@ interface String {
     concat(...strings: string[]): string;
 
     /**
-      * Returns the position of the first occurrence of a substring. 
+      * Returns the position of the first occurrence of a substring, or -1 if it is not present.
       * @param searchString The substring to search for in the string
       * @param position The index at which to begin searching the String object. If omitted, search starts at the beginning of the string.
       */
     indexOf(searchString: string, position?: number): number;
 
     /**
-      * Returns the last occurrence of a substring in the string.
+      * Returns the last occurrence of a substring in the string, or -1 if it is not present.
       * @param searchString The substring to search for.
       * @param position The index at which to begin searching. If omitted, the search begins at the end of the string.
       */
@@ -1143,7 +1143,8 @@ declare var Array: {
     <T>(...items: T[]): T[];
     isArray(arg: any): boolean;
     prototype: Array<any>;
-}

+}
+
 
 //// [1.0lib-noErrors.js]
 /* *****************************************************************************
diff --git a/tests/baselines/reference/1.0lib-noErrors.symbols b/tests/baselines/reference/1.0lib-noErrors.symbols
index 5ac0014e33ed1..2b0cef1ee8f89 100644
--- a/tests/baselines/reference/1.0lib-noErrors.symbols
+++ b/tests/baselines/reference/1.0lib-noErrors.symbols
@@ -440,7 +440,7 @@ interface String {
 >strings : Symbol(strings, Decl(1.0lib-noErrors.ts, 293, 11))
 
     /**
-      * Returns the position of the first occurrence of a substring. 
+      * Returns the position of the first occurrence of a substring, or -1 if it is not present.
       * @param searchString The substring to search for in the string
       * @param position The index at which to begin searching the String object. If omitted, search starts at the beginning of the string.
       */
@@ -450,7 +450,7 @@ interface String {
 >position : Symbol(position, Decl(1.0lib-noErrors.ts, 300, 33))
 
     /**
-      * Returns the last occurrence of a substring in the string.
+      * Returns the last occurrence of a substring in the string, or -1 if it is not present.
       * @param searchString The substring to search for.
       * @param position The index at which to begin searching. If omitted, the search begins at the end of the string.
       */
diff --git a/tests/baselines/reference/1.0lib-noErrors.types b/tests/baselines/reference/1.0lib-noErrors.types
index f7d94356d476b..d36516c82e1ab 100644
--- a/tests/baselines/reference/1.0lib-noErrors.types
+++ b/tests/baselines/reference/1.0lib-noErrors.types
@@ -491,7 +491,7 @@ interface String {
 >        : ^^^^^^^^
 
     /**
-      * Returns the position of the first occurrence of a substring. 
+      * Returns the position of the first occurrence of a substring, or -1 if it is not present.
       * @param searchString The substring to search for in the string
       * @param position The index at which to begin searching the String object. If omitted, search starts at the beginning of the string.
       */
@@ -504,7 +504,7 @@ interface String {
 >         : ^^^^^^
 
     /**
-      * Returns the last occurrence of a substring in the string.
+      * Returns the last occurrence of a substring in the string, or -1 if it is not present.
       * @param searchString The substring to search for.
       * @param position The index at which to begin searching. If omitted, the search begins at the end of the string.
       */
diff --git a/tests/baselines/reference/completionsStringMethods.baseline b/tests/baselines/reference/completionsStringMethods.baseline
index bf00835b43760..c1b618086f6f1 100644
--- a/tests/baselines/reference/completionsStringMethods.baseline
+++ b/tests/baselines/reference/completionsStringMethods.baseline
@@ -443,7 +443,7 @@
           ],
           "documentation": [
             {
-              "text": "Returns the position of the first occurrence of a substring.",
+              "text": "Returns the position of the first occurrence of a substring, or -1 if it is not present.",
               "kind": "text"
             }
           ],
@@ -585,7 +585,7 @@
           ],
           "documentation": [
             {
-              "text": "Returns the last occurrence of a substring in the string.",
+              "text": "Returns the last occurrence of a substring in the string, or -1 if it is not present.",
               "kind": "text"
             }
           ],
diff --git a/tests/cases/conformance/decorators/1.0lib-noErrors.ts b/tests/cases/conformance/decorators/1.0lib-noErrors.ts
index e170df0c9bf6a..02de2d9aa0d16 100644
--- a/tests/cases/conformance/decorators/1.0lib-noErrors.ts
+++ b/tests/cases/conformance/decorators/1.0lib-noErrors.ts
@@ -295,14 +295,14 @@ interface String {
     concat(...strings: string[]): string;
 
     /**
-      * Returns the position of the first occurrence of a substring. 
+      * Returns the position of the first occurrence of a substring, or -1 if it is not present.
       * @param searchString The substring to search for in the string
       * @param position The index at which to begin searching the String object. If omitted, search starts at the beginning of the string.
       */
     indexOf(searchString: string, position?: number): number;
 
     /**
-      * Returns the last occurrence of a substring in the string.
+      * Returns the last occurrence of a substring in the string, or -1 if it is not present.
       * @param searchString The substring to search for.
       * @param position The index at which to begin searching. If omitted, the search begins at the end of the string.
       */
@@ -1141,4 +1141,4 @@ declare var Array: {
     <T>(...items: T[]): T[];
     isArray(arg: any): boolean;
     prototype: Array<any>;
-}
\ No newline at end of file
+}