diff --git a/types/jest-when/index.d.ts b/types/jest-when/index.d.ts
index 9a9fb9a55f..f7df56a507 100644
--- a/types/jest-when/index.d.ts
+++ b/types/jest-when/index.d.ts
@@ -1,6 +1,7 @@
-// Type definitions for jest-when 1.1
+// Type definitions for jest-when 2.4
 // Project: https://github.com/timkindberg/jest-when#readme
 // Definitions by: Alden Taylor <https://github.com/aldentaylor>
+//                 Trung Dang <https://github.com/immanuel192>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 // TypeScript Version: 3.0
 
@@ -15,6 +16,8 @@ export interface WhenMock<T = any, Y extends any[] = any> extends jest.Mock<T, Y
   mockResolvedValueOnce(value: jest.ResolvedValue<T>): WhenMock<T, Y>;
   mockRejectedValue(value: jest.RejectedValue<T>): WhenMock<T, Y>;
   mockRejectedValueOnce(value: jest.RejectedValue<T>): WhenMock<T, Y>;
+  mockImplementation(fn: (...args: Y) => T): WhenMock<T, Y>;
+  mockImplementationOnce(fn?: (...args: Y) => T): WhenMock<T, Y>;
 }
 
 export type When = <T, Y extends any[]>(fn: jest.Mock<T, Y>) => WhenMock<T, Y>;
diff --git a/types/jest-when/jest-when-tests.ts b/types/jest-when/jest-when-tests.ts
index 55744218ce..e37021e983 100644
--- a/types/jest-when/jest-when-tests.ts
+++ b/types/jest-when/jest-when-tests.ts
@@ -89,4 +89,28 @@ describe('mock-when test', () => {
     }
     expect(testPassed).toBeTruthy();
   });
+
+  it('should support for mockImplementation', () => {
+    const fn = jest.fn();
+    const expectValue = { a: 1, b: 2 };
+    when(fn).calledWith(
+      expect.anything()
+    ).mockImplementation(() => (expectValue));
+
+    const result = fn('whatever');
+    expect(result).toMatchObject(expectValue);
+  });
+
+  it('should support for mockImplementationOnce', () => {
+    const fn = jest.fn();
+    const expectValue = { a: 1, b: 2 };
+    when(fn).calledWith(
+      expect.anything()
+    ).mockImplementationOnce(() => (expectValue));
+
+    const result = fn('whatever');
+    const result2 = fn('whatever');
+    expect(result).toMatchObject(expectValue);
+    expect(result2).toEqual(undefined);
+  });
 });