diff --git a/types/when/index.d.ts b/types/when/index.d.ts
index 3736cfa7dd..0b016a9ea0 100644
--- a/types/when/index.d.ts
+++ b/types/when/index.d.ts
@@ -285,11 +285,11 @@ declare namespace When {
         // be a constructor with prototype set to an instance of Error.
         otherwise<U>(exceptionType: any, onRejected?: (reason: any) => U | Promise<U>): Promise<U>;
 
-        then(
-            onFulfilled?: ((value: T) => T | Thenable<T>) | undefined | null,
-            onRejected?: ((reason: any) => T | Thenable<T>) | undefined | null,
+        then<TResult1, TResult2>(
+            onFulfilled: ((value: T) => TResult1 | Thenable<TResult1>),
+            onRejected: ((reason: any) => TResult2 | Thenable<TResult2>),
             onProgress?: (update: any) => void
-        ): Promise<T>;
+        ): Promise<TResult1 | TResult2>;
         then<TResult>(
             onFulfilled: ((value: T) => TResult | Thenable<TResult>),
             onRejected?: ((reason: any) => TResult | Thenable<TResult>) | undefined | null,
@@ -300,11 +300,11 @@ declare namespace When {
             onRejected: ((reason: any) => TResult | Thenable<TResult>),
             onProgress?: (update: any) => void
         ): Promise<T | TResult>;
-        then<TResult1, TResult2>(
-            onFulfilled: ((value: T) => TResult1 | Thenable<TResult1>),
-            onRejected: ((reason: any) => TResult2 | Thenable<TResult2>),
+        then(
+            onFulfilled?: ((value: T) => T | Thenable<T>) | undefined | null,
+            onRejected?: ((reason: any) => T | Thenable<T>) | undefined | null,
             onProgress?: (update: any) => void
-        ): Promise<TResult1 | TResult2>;
+        ): Promise<T>;
 
         spread<T>(onFulfilled: _.Fn0<Promise<T> | T>): Promise<T>;
         spread<A1, T>(onFulfilled: _.Fn1<A1, Promise<T> | T>): Promise<T>;
diff --git a/types/when/tsconfig.json b/types/when/tsconfig.json
index 2162d713fc..84a5f78c14 100644
--- a/types/when/tsconfig.json
+++ b/types/when/tsconfig.json
@@ -1,6 +1,7 @@
 {
     "compilerOptions": {
         "module": "commonjs",
+        "target": "es5",
         "lib": [
             "es6"
         ],
diff --git a/types/when/when-tests.ts b/types/when/when-tests.ts
index d44752b950..e1e3f0fd7c 100644
--- a/types/when/when-tests.ts
+++ b/types/when/when-tests.ts
@@ -14,9 +14,24 @@ class ForeignPromise<T> {
 	then(onFulfilled?: (value: T) => T, onRejected?: (reason: any) => T): ForeignPromise<T> {
 		return new ForeignPromise(onFulfilled ? onFulfilled(this.value) : this.value);
 	}
-};
+}
+
+interface IData {
+	timestamp: number;
+}
+
+class Data implements IData {
+	timestamp: number;
+	date: Date;
+
+	constructor({ timestamp }: IData) {
+		this.timestamp = timestamp;
+		this.date = new Date(timestamp);
+	}
+}
 
 var promise: when.Promise<number>;
+var promise2: when.Promise<Data>;
 var foreign = new ForeignPromise<number>(1);
 var error = new Error("boom!");
 var example: () => void;
@@ -222,6 +237,17 @@ promise = when(1).then(undefined, (err: any) => 2);
 promise = when(1).then((val: number) => val + val, (err: any) => 2);
 promise = when(1).then((val: number) => when(val + val), (err: any) => 2);
 
+promise = when('1').then((val: string) => parseInt(val));
+
+// Tests for when TResult is a subtype of T
+const subData: IData = { timestamp: Date.now() };
+const errorData: Data = new Data({ timestamp: -1 });
+
+promise2 = when(subData).then((val: IData) => new Data(val));
+promise2 = when(subData).then((val: IData) => when(new Data(val)));
+promise2 = when(subData).then((val: IData) => new Data(val), (err: any) => errorData);
+promise2 = when(subData).then((val: IData) => when(new Data(val)), (err: any) => errorData);
+
 /* promise.spread(onFulfilledArray) */
 
 promise = when([]).spread(() => 2);