diff --git a/src/lib/es2015.core.d.ts b/src/lib/es2015.core.d.ts
index cfb300c784d74..09933b4ca7575 100644
--- a/src/lib/es2015.core.d.ts
+++ b/src/lib/es2015.core.d.ts
@@ -256,6 +256,10 @@ interface NumberConstructor {
     parseInt(string: string, radix?: number): number;
 }
 
+type Key<T> = {
+  [K in keyof T]: K extends string ? K : (K extends number ? string : never)
+}[keyof T];
+
 interface ObjectConstructor {
     /**
      * Copy the values of all of the enumerable own properties from one or more source objects to a
@@ -298,6 +302,12 @@ interface ObjectConstructor {
      */
     getOwnPropertySymbols(o: any): symbol[];
 
+    /**
+      * Returns the names of the enumerable string properties and methods of an object.
+      * @param o Object that contains the properties and methods. This can be an object that you created or an existing Document Object Model (DOM) object.
+      */
+    keys<T = {}>(o: T): Key<T>[];
+
     /**
      * Returns true if the values are the same value, false otherwise.
      * @param value1 The first value.
diff --git a/src/lib/es5.d.ts b/src/lib/es5.d.ts
index 308af721af625..5c31892846a17 100644
--- a/src/lib/es5.d.ts
+++ b/src/lib/es5.d.ts
@@ -129,6 +129,10 @@ interface Object {
     propertyIsEnumerable(v: PropertyKey): boolean;
 }
 
+type Key<T> = {
+  [K in keyof T]: K extends string ? K : (K extends number ? string : never)
+}[keyof T];
+
 interface ObjectConstructor {
     new(value?: any): Object;
     (): any;
@@ -235,10 +239,10 @@ interface ObjectConstructor {
     isExtensible(o: any): boolean;
 
     /**
-      * Returns the names of the enumerable properties and methods of an object.
+      * Returns the names of the enumerable string properties and methods of an object.
       * @param o Object that contains the properties and methods. This can be an object that you created or an existing Document Object Model (DOM) object.
       */
-    keys(o: {}): string[];
+    keys<T = {}>(o: T): Key<T>[];
 }
 
 /**
diff --git a/tests/baselines/reference/contextualExpressionTypecheckingDoesntBlowStack.symbols b/tests/baselines/reference/contextualExpressionTypecheckingDoesntBlowStack.symbols
index fc44c97996c92..60dfdd9983ae3 100644
--- a/tests/baselines/reference/contextualExpressionTypecheckingDoesntBlowStack.symbols
+++ b/tests/baselines/reference/contextualExpressionTypecheckingDoesntBlowStack.symbols
@@ -21,9 +21,9 @@ export default class Operation {
 
         for(const parameterLocation of Object.keys(parameterValues)) {
 >parameterLocation : Symbol(parameterLocation, Decl(contextualExpressionTypecheckingDoesntBlowStack.ts, 8, 17))
->Object.keys : Symbol(ObjectConstructor.keys, Decl(lib.es5.d.ts, --, --))
+>Object.keys : Symbol(ObjectConstructor.keys, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --))
 >Object : Symbol(Object, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
->keys : Symbol(ObjectConstructor.keys, Decl(lib.es5.d.ts, --, --))
+>keys : Symbol(ObjectConstructor.keys, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --))
 >parameterValues : Symbol(parameterValues, Decl(contextualExpressionTypecheckingDoesntBlowStack.ts, 6, 23))
 
             const parameter: any = (this as any).getParameter();;
diff --git a/tests/baselines/reference/contextualExpressionTypecheckingDoesntBlowStack.types b/tests/baselines/reference/contextualExpressionTypecheckingDoesntBlowStack.types
index 8d462f4dbd912..3e690f0844b1d 100644
--- a/tests/baselines/reference/contextualExpressionTypecheckingDoesntBlowStack.types
+++ b/tests/baselines/reference/contextualExpressionTypecheckingDoesntBlowStack.types
@@ -21,9 +21,9 @@ export default class Operation {
         for(const parameterLocation of Object.keys(parameterValues)) {
 >parameterLocation : string
 >Object.keys(parameterValues) : string[]
->Object.keys : (o: {}) => string[]
+>Object.keys : { (o: object): string[]; (o: {}): string[]; }
 >Object : ObjectConstructor
->keys : (o: {}) => string[]
+>keys : { (o: object): string[]; (o: {}): string[]; }
 >parameterValues : any
 
             const parameter: any = (this as any).getParameter();;
diff --git a/tests/baselines/reference/genericIndexedAccessMethodIntersectionCanBeAccessed.types b/tests/baselines/reference/genericIndexedAccessMethodIntersectionCanBeAccessed.types
index d16a75912f491..f5d2f78e0f6c7 100644
--- a/tests/baselines/reference/genericIndexedAccessMethodIntersectionCanBeAccessed.types
+++ b/tests/baselines/reference/genericIndexedAccessMethodIntersectionCanBeAccessed.types
@@ -32,9 +32,9 @@ export const createService = <T>(
 >Object.keys(ServiceCtr).forEach(key => {        const method = (ServiceCtr)[key as keyof T];        const {__$daemonMode, __$action, id} = method;    }) : void
 >Object.keys(ServiceCtr).forEach : (callbackfn: (value: string, index: number, array: string[]) => void, thisArg?: any) => void
 >Object.keys(ServiceCtr) : string[]
->Object.keys : (o: {}) => string[]
+>Object.keys : (o: object) => string[]
 >Object : ObjectConstructor
->keys : (o: {}) => string[]
+>keys : (o: object) => string[]
 >ServiceCtr : ExtendedService<T> & Service<T>
 >forEach : (callbackfn: (value: string, index: number, array: string[]) => void, thisArg?: any) => void
 >key => {        const method = (ServiceCtr)[key as keyof T];        const {__$daemonMode, __$action, id} = method;    } : (key: string) => void
diff --git a/tests/baselines/reference/literalTypeWidening.types b/tests/baselines/reference/literalTypeWidening.types
index a96ddc8c5da3e..95bde9a08ac3d 100644
--- a/tests/baselines/reference/literalTypeWidening.types
+++ b/tests/baselines/reference/literalTypeWidening.types
@@ -391,9 +391,9 @@ export function keys<K extends string, V>(obj: Record<K, V>): K[] {
   return Object.keys(obj) as K[]
 >Object.keys(obj) as K[] : K[]
 >Object.keys(obj) : string[]
->Object.keys : (o: {}) => string[]
+>Object.keys : (o: object) => string[]
 >Object : ObjectConstructor
->keys : (o: {}) => string[]
+>keys : (o: object) => string[]
 >obj : Record<K, V>
 }
 
diff --git a/tests/baselines/reference/recursiveTypeRelations.types b/tests/baselines/reference/recursiveTypeRelations.types
index cb0baef7919d6..669ab3879c4fc 100644
--- a/tests/baselines/reference/recursiveTypeRelations.types
+++ b/tests/baselines/reference/recursiveTypeRelations.types
@@ -72,9 +72,9 @@ export function css<S extends { [K in keyof S]: string }>(styles: S, ...classNam
 >Object.keys(arg).reduce<ClassNameObject>((obj: ClassNameObject, key: keyof S) => {        const exportedClassName = styles[key];        obj[exportedClassName] = (arg as ClassNameMap<S>)[key];         return obj;      }, {}) : any
 >Object.keys(arg).reduce : { (callbackfn: (previousValue: string, currentValue: string, currentIndex: number, array: string[]) => string): string; (callbackfn: (previousValue: string, currentValue: string, currentIndex: number, array: string[]) => string, initialValue: string): string; <U>(callbackfn: (previousValue: U, currentValue: string, currentIndex: number, array: string[]) => U, initialValue: U): U; }
 >Object.keys(arg) : string[]
->Object.keys : (o: {}) => string[]
+>Object.keys : (o: object) => string[]
 >Object : ObjectConstructor
->keys : (o: {}) => string[]
+>keys : (o: object) => string[]
 >arg : ClassNameObjectMap<S>
 >reduce : { (callbackfn: (previousValue: string, currentValue: string, currentIndex: number, array: string[]) => string): string; (callbackfn: (previousValue: string, currentValue: string, currentIndex: number, array: string[]) => string, initialValue: string): string; <U>(callbackfn: (previousValue: U, currentValue: string, currentIndex: number, array: string[]) => U, initialValue: U): U; }
 >(obj: ClassNameObject, key: keyof S) => {        const exportedClassName = styles[key];        obj[exportedClassName] = (arg as ClassNameMap<S>)[key];         return obj;      } : (obj: any, key: keyof S) => any
diff --git a/tests/baselines/reference/taggedTemplateStringsWithOverloadResolution3_ES6.errors.txt b/tests/baselines/reference/taggedTemplateStringsWithOverloadResolution3_ES6.errors.txt
index a4ba377af29fd..c5063689b51b4 100644
--- a/tests/baselines/reference/taggedTemplateStringsWithOverloadResolution3_ES6.errors.txt
+++ b/tests/baselines/reference/taggedTemplateStringsWithOverloadResolution3_ES6.errors.txt
@@ -89,7 +89,7 @@ tests/cases/conformance/es6/templates/taggedTemplateStringsWithOverloadResolutio
     fn5 `${ (n) => n.toFixed() }`; // will error; 'n' should have type 'string'.
                      ~~~~~~~
 !!! error TS2551: Property 'toFixed' does not exist on type 'string'. Did you mean 'fixed'?
-!!! related TS2728 /.ts/lib.es2015.core.d.ts:466:5: 'fixed' is declared here.
+!!! related TS2728 /.ts/lib.es2015.core.d.ts:472:5: 'fixed' is declared here.
     fn5 `${ (n) => n.substr(0) }`;
     
     
\ No newline at end of file