diff --git a/lodash/lodash-tests.ts b/lodash/lodash-tests.ts
index 4c587b57b..319729237 100644
--- a/lodash/lodash-tests.ts
+++ b/lodash/lodash-tests.ts
@@ -5259,13 +5259,48 @@ module TestFindLastKey {
     }
 }
 
-result = <Dog>_.forIn(new Dog('Dagny'), function (value, key) {
-    console.log(key);
-});
+// _.forIn
+module TestForIn {
+    type SampleObject = {a: number; b: string; c: boolean;};
 
-result = <_.LoDashImplicitObjectWrapper<Dog>>_(new Dog('Dagny')).forIn(function (value, key) {
-    console.log(key);
-});
+    let dictionary: _.Dictionary<number>;
+    let dictionaryIterator: (value: number, key: string, collection: _.Dictionary<number>) => any;
+
+    let object: SampleObject;
+    let objectIterator: (element: any, key?: string, collection?: any) => any;
+
+    {
+        let result: _.Dictionary<number>;
+
+        result = _.forIn<number>(dictionary);
+        result = _.forIn<number>(dictionary, dictionaryIterator);
+        result = _.forIn<number>(dictionary, dictionaryIterator, any);
+    }
+
+    {
+        let result: SampleObject;
+
+        result = _.forIn<SampleObject>(object);
+        result = _.forIn<SampleObject>(object, objectIterator);
+        result = _.forIn<SampleObject>(object, objectIterator, any);
+    }
+
+    {
+        let result: _.LoDashImplicitObjectWrapper<_.Dictionary<number>>;
+
+        result = _(dictionary).forIn<number>();
+        result = _(dictionary).forIn<number>(dictionaryIterator);
+        result = _(dictionary).forIn<number>(dictionaryIterator, any);
+    }
+
+    {
+        let result: _.LoDashExplicitObjectWrapper<_.Dictionary<number>>;
+
+        result = _(dictionary).chain().forIn<number>();
+        result = _(dictionary).chain().forIn<number>(dictionaryIterator);
+        result = _(dictionary).chain().forIn<number>(dictionaryIterator, any);
+    }
+}
 
 result = <Dog>_.forInRight(new Dog('Dagny'), function (value, key) {
     console.log(key);
diff --git a/lodash/lodash.d.ts b/lodash/lodash.d.ts
index 98d8bf55d..a46d9642c 100644
--- a/lodash/lodash.d.ts
+++ b/lodash/lodash.d.ts
@@ -9936,35 +9936,49 @@ declare module _ {
     //_.forIn
     interface LoDashStatic {
         /**
-        * Iterates over own and inherited enumerable properties of an object, executing the callback for
-        * each property. The callback is bound to thisArg and invoked with three arguments; (value, key,
-        * object). Callbacks may exit iteration early by explicitly returning false.
-        * @param object The object to iterate over.
-        * @param callback The function called per iteration.
-        * @param thisArg The this binding of callback.
-        * @return object
-        **/
+         * Iterates over own and inherited enumerable properties of an object invoking iteratee for each property. The
+         * iteratee is bound to thisArg and invoked with three arguments: (value, key, object). Iteratee functions may
+         * exit iteration early by explicitly returning false.
+         *
+         * @param object The object to iterate over.
+         * @param iteratee The function invoked per iteration.
+         * @param thisArg The this binding of iteratee.
+         * @return Returns object.
+         */
         forIn<T>(
             object: Dictionary<T>,
-            callback?: DictionaryIterator<T, void>,
-            thisArg?: any): Dictionary<T>;
+            iteratee?: DictionaryIterator<T, any>,
+            thisArg?: any
+        ): Dictionary<T>;
 
         /**
-        * @see _.forIn
-        **/
-        forIn<T>(
+         * @see _.forIn
+         */
+        forIn<T extends {}>(
             object: T,
-            callback?: ObjectIterator<any, void>,
-            thisArg?: any): T;
+            iteratee?: ObjectIterator<any, any>,
+            thisArg?: any
+        ): T;
     }
 
     interface LoDashImplicitObjectWrapper<T> {
         /**
-        * @see _.forIn
-        **/
-        forIn<T extends {}>(
-            callback: ObjectIterator<T, void>,
-            thisArg?: any): _.LoDashImplicitObjectWrapper<T>;
+         * @see _.forIn
+         */
+        forIn<TValue>(
+            iteratee?: DictionaryIterator<TValue, any>,
+            thisArg?: any
+        ): _.LoDashImplicitObjectWrapper<T>;
+    }
+
+    interface LoDashExplicitObjectWrapper<T> {
+        /**
+         * @see _.forIn
+         */
+        forIn<TValue>(
+            iteratee?: DictionaryIterator<TValue, any>,
+            thisArg?: any
+        ): _.LoDashExplicitObjectWrapper<T>;
     }
 
     //_.forInRight