diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index e935895649b..24ca7da87c4 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -15146,8 +15146,8 @@ namespace ts {
             else {
                 let types: Type[];
                 if (functionFlags & FunctionFlags.Generator) { // Generator or AsyncGenerator function
-                    types = checkAndAggregateYieldOperandTypes(func, checkMode);
-                    if (types.length === 0) {
+                    types = concatenate(checkAndAggregateYieldOperandTypes(func, checkMode), checkAndAggregateReturnExpressionTypes(func, checkMode));
+                    if (!types || types.length === 0) {
                         const iterableIteratorAny = functionFlags & FunctionFlags.Async
                             ? createAsyncIterableIteratorType(anyType) // AsyncGenerator function
                             : createIterableIteratorType(anyType); // Generator function
diff --git a/tests/baselines/reference/emitter.asyncGenerators.classMethods.es2015.types b/tests/baselines/reference/emitter.asyncGenerators.classMethods.es2015.types
index 524f7c9b71b..c375fb6f455 100644
--- a/tests/baselines/reference/emitter.asyncGenerators.classMethods.es2015.types
+++ b/tests/baselines/reference/emitter.asyncGenerators.classMethods.es2015.types
@@ -80,7 +80,7 @@ class C7 {
 >C7 : C7
 
     async * f() {
->f : () => AsyncIterableIterator<any>
+>f : () => AsyncIterableIterator<1>
 
         return 1;
 >1 : 1
diff --git a/tests/baselines/reference/emitter.asyncGenerators.classMethods.es5.types b/tests/baselines/reference/emitter.asyncGenerators.classMethods.es5.types
index c20e0d35010..e4be9f80d4a 100644
--- a/tests/baselines/reference/emitter.asyncGenerators.classMethods.es5.types
+++ b/tests/baselines/reference/emitter.asyncGenerators.classMethods.es5.types
@@ -80,7 +80,7 @@ class C7 {
 >C7 : C7
 
     async * f() {
->f : () => AsyncIterableIterator<any>
+>f : () => AsyncIterableIterator<1>
 
         return 1;
 >1 : 1
diff --git a/tests/baselines/reference/emitter.asyncGenerators.classMethods.esnext.types b/tests/baselines/reference/emitter.asyncGenerators.classMethods.esnext.types
index b5230006f1b..1232130a389 100644
--- a/tests/baselines/reference/emitter.asyncGenerators.classMethods.esnext.types
+++ b/tests/baselines/reference/emitter.asyncGenerators.classMethods.esnext.types
@@ -80,7 +80,7 @@ class C7 {
 >C7 : C7
 
     async * f() {
->f : () => AsyncIterableIterator<any>
+>f : () => AsyncIterableIterator<1>
 
         return 1;
 >1 : 1
diff --git a/tests/baselines/reference/emitter.asyncGenerators.functionDeclarations.es2015.types b/tests/baselines/reference/emitter.asyncGenerators.functionDeclarations.es2015.types
index 5d57519d140..0e434639906 100644
--- a/tests/baselines/reference/emitter.asyncGenerators.functionDeclarations.es2015.types
+++ b/tests/baselines/reference/emitter.asyncGenerators.functionDeclarations.es2015.types
@@ -53,7 +53,7 @@ async function * f6() {
 }
 === tests/cases/conformance/emitter/es2015/asyncGenerators/F7.ts ===
 async function * f7() {
->f7 : () => AsyncIterableIterator<any>
+>f7 : () => AsyncIterableIterator<1>
 
     return 1;
 >1 : 1
diff --git a/tests/baselines/reference/emitter.asyncGenerators.functionDeclarations.es5.types b/tests/baselines/reference/emitter.asyncGenerators.functionDeclarations.es5.types
index 2c3063eca59..9ebd2659ef4 100644
--- a/tests/baselines/reference/emitter.asyncGenerators.functionDeclarations.es5.types
+++ b/tests/baselines/reference/emitter.asyncGenerators.functionDeclarations.es5.types
@@ -53,7 +53,7 @@ async function * f6() {
 }
 === tests/cases/conformance/emitter/es5/asyncGenerators/F7.ts ===
 async function * f7() {
->f7 : () => AsyncIterableIterator<any>
+>f7 : () => AsyncIterableIterator<1>
 
     return 1;
 >1 : 1
diff --git a/tests/baselines/reference/emitter.asyncGenerators.functionDeclarations.esnext.types b/tests/baselines/reference/emitter.asyncGenerators.functionDeclarations.esnext.types
index 5eb09901ac8..4e61c903227 100644
--- a/tests/baselines/reference/emitter.asyncGenerators.functionDeclarations.esnext.types
+++ b/tests/baselines/reference/emitter.asyncGenerators.functionDeclarations.esnext.types
@@ -53,7 +53,7 @@ async function * f6() {
 }
 === tests/cases/conformance/emitter/esnext/asyncGenerators/F7.ts ===
 async function * f7() {
->f7 : () => AsyncIterableIterator<any>
+>f7 : () => AsyncIterableIterator<1>
 
     return 1;
 >1 : 1
diff --git a/tests/baselines/reference/emitter.asyncGenerators.functionExpressions.es2015.types b/tests/baselines/reference/emitter.asyncGenerators.functionExpressions.es2015.types
index ab41ffd9c71..83d65ce5246 100644
--- a/tests/baselines/reference/emitter.asyncGenerators.functionExpressions.es2015.types
+++ b/tests/baselines/reference/emitter.asyncGenerators.functionExpressions.es2015.types
@@ -59,8 +59,8 @@ const f6 = async function * () {
 }
 === tests/cases/conformance/emitter/es2015/asyncGenerators/F7.ts ===
 const f7 = async function * () {
->f7 : () => AsyncIterableIterator<any>
->async function * () {    return 1;} : () => AsyncIterableIterator<any>
+>f7 : () => AsyncIterableIterator<1>
+>async function * () {    return 1;} : () => AsyncIterableIterator<1>
 
     return 1;
 >1 : 1
diff --git a/tests/baselines/reference/emitter.asyncGenerators.functionExpressions.es5.types b/tests/baselines/reference/emitter.asyncGenerators.functionExpressions.es5.types
index 424f09cf53b..7d736b2327c 100644
--- a/tests/baselines/reference/emitter.asyncGenerators.functionExpressions.es5.types
+++ b/tests/baselines/reference/emitter.asyncGenerators.functionExpressions.es5.types
@@ -59,8 +59,8 @@ const f6 = async function * () {
 }
 === tests/cases/conformance/emitter/es5/asyncGenerators/F7.ts ===
 const f7 = async function * () {
->f7 : () => AsyncIterableIterator<any>
->async function * () {    return 1;} : () => AsyncIterableIterator<any>
+>f7 : () => AsyncIterableIterator<1>
+>async function * () {    return 1;} : () => AsyncIterableIterator<1>
 
     return 1;
 >1 : 1
diff --git a/tests/baselines/reference/emitter.asyncGenerators.functionExpressions.esnext.types b/tests/baselines/reference/emitter.asyncGenerators.functionExpressions.esnext.types
index e4559e3ecef..6c40f9cebb1 100644
--- a/tests/baselines/reference/emitter.asyncGenerators.functionExpressions.esnext.types
+++ b/tests/baselines/reference/emitter.asyncGenerators.functionExpressions.esnext.types
@@ -59,8 +59,8 @@ const f6 = async function * () {
 }
 === tests/cases/conformance/emitter/esnext/asyncGenerators/F7.ts ===
 const f7 = async function * () {
->f7 : () => AsyncIterableIterator<any>
->async function * () {    return 1;} : () => AsyncIterableIterator<any>
+>f7 : () => AsyncIterableIterator<1>
+>async function * () {    return 1;} : () => AsyncIterableIterator<1>
 
     return 1;
 >1 : 1
diff --git a/tests/baselines/reference/emitter.asyncGenerators.objectLiteralMethods.es2015.types b/tests/baselines/reference/emitter.asyncGenerators.objectLiteralMethods.es2015.types
index 0e89d9a1ca6..59c5bcfa167 100644
--- a/tests/baselines/reference/emitter.asyncGenerators.objectLiteralMethods.es2015.types
+++ b/tests/baselines/reference/emitter.asyncGenerators.objectLiteralMethods.es2015.types
@@ -83,11 +83,11 @@ const o6 = {
 }
 === tests/cases/conformance/emitter/es2015/asyncGenerators/O7.ts ===
 const o7 = {
->o7 : { f(): AsyncIterableIterator<any>; }
->{    async * f() {        return 1;    }} : { f(): AsyncIterableIterator<any>; }
+>o7 : { f(): AsyncIterableIterator<1>; }
+>{    async * f() {        return 1;    }} : { f(): AsyncIterableIterator<1>; }
 
     async * f() {
->f : () => AsyncIterableIterator<any>
+>f : () => AsyncIterableIterator<1>
 
         return 1;
 >1 : 1
diff --git a/tests/baselines/reference/emitter.asyncGenerators.objectLiteralMethods.es5.types b/tests/baselines/reference/emitter.asyncGenerators.objectLiteralMethods.es5.types
index 4c8ae47b6a2..3e7ead2f737 100644
--- a/tests/baselines/reference/emitter.asyncGenerators.objectLiteralMethods.es5.types
+++ b/tests/baselines/reference/emitter.asyncGenerators.objectLiteralMethods.es5.types
@@ -83,11 +83,11 @@ const o6 = {
 }
 === tests/cases/conformance/emitter/es5/asyncGenerators/O7.ts ===
 const o7 = {
->o7 : { f(): AsyncIterableIterator<any>; }
->{    async * f() {        return 1;    }} : { f(): AsyncIterableIterator<any>; }
+>o7 : { f(): AsyncIterableIterator<1>; }
+>{    async * f() {        return 1;    }} : { f(): AsyncIterableIterator<1>; }
 
     async * f() {
->f : () => AsyncIterableIterator<any>
+>f : () => AsyncIterableIterator<1>
 
         return 1;
 >1 : 1
diff --git a/tests/baselines/reference/emitter.asyncGenerators.objectLiteralMethods.esnext.types b/tests/baselines/reference/emitter.asyncGenerators.objectLiteralMethods.esnext.types
index 511cd7ec9e0..9e5aad8af23 100644
--- a/tests/baselines/reference/emitter.asyncGenerators.objectLiteralMethods.esnext.types
+++ b/tests/baselines/reference/emitter.asyncGenerators.objectLiteralMethods.esnext.types
@@ -83,11 +83,11 @@ const o6 = {
 }
 === tests/cases/conformance/emitter/esnext/asyncGenerators/O7.ts ===
 const o7 = {
->o7 : { f(): AsyncIterableIterator<any>; }
->{    async * f() {        return 1;    }} : { f(): AsyncIterableIterator<any>; }
+>o7 : { f(): AsyncIterableIterator<1>; }
+>{    async * f() {        return 1;    }} : { f(): AsyncIterableIterator<1>; }
 
     async * f() {
->f : () => AsyncIterableIterator<any>
+>f : () => AsyncIterableIterator<1>
 
         return 1;
 >1 : 1
diff --git a/tests/baselines/reference/generatorTypeCheck14.types b/tests/baselines/reference/generatorTypeCheck14.types
index 48565fe2be0..28401e68567 100644
--- a/tests/baselines/reference/generatorTypeCheck14.types
+++ b/tests/baselines/reference/generatorTypeCheck14.types
@@ -1,6 +1,6 @@
 === tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck14.ts ===
 function* g() {
->g : () => IterableIterator<0>
+>g : () => IterableIterator<0 | "">
 
     yield 0;
 >yield 0 : any
diff --git a/tests/baselines/reference/generatorTypeCheck15.types b/tests/baselines/reference/generatorTypeCheck15.types
index eb14208009a..3851d8e56a4 100644
--- a/tests/baselines/reference/generatorTypeCheck15.types
+++ b/tests/baselines/reference/generatorTypeCheck15.types
@@ -1,6 +1,6 @@
 === tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck15.ts ===
 function* g() {
->g : () => IterableIterator<any>
+>g : () => IterableIterator<"">
 
     return "";
 >"" : ""
diff --git a/tests/baselines/reference/generatorTypeCheck34.types b/tests/baselines/reference/generatorTypeCheck34.types
index 2ca11177218..239c5ff1493 100644
--- a/tests/baselines/reference/generatorTypeCheck34.types
+++ b/tests/baselines/reference/generatorTypeCheck34.types
@@ -7,7 +7,7 @@ function* g() {
 >0 : 0
 
     function* g2() {
->g2 : () => IterableIterator<any>
+>g2 : () => IterableIterator<"">
 
         return "";
 >"" : ""
diff --git a/tests/baselines/reference/generatorTypeCheck62.js b/tests/baselines/reference/generatorTypeCheck62.js
new file mode 100644
index 00000000000..30864722210
--- /dev/null
+++ b/tests/baselines/reference/generatorTypeCheck62.js
@@ -0,0 +1,63 @@
+//// [generatorTypeCheck62.ts]
+
+export interface StrategicState {
+    lastStrategyApplied?: string;
+}
+
+export function strategy<T extends StrategicState>(stratName: string, gen: (a: T) => IterableIterator<T | undefined>): (a: T) => IterableIterator<T | undefined> {
+    return function*(state) {
+        for (const next of gen(state)) {
+            if (next) {
+                next.lastStrategyApplied = stratName;
+            }
+            yield next;
+        }
+    }
+}
+
+export interface Strategy<T> {
+    (a: T): IterableIterator<T | undefined>;
+}
+
+export interface State extends StrategicState {
+    foo: number;
+}
+
+export const Nothing1: Strategy<State> = strategy("Nothing", function*(state: State) {
+    return state;
+});
+
+export const Nothing2: Strategy<State> = strategy("Nothing", function*(state: State) {
+    yield state;
+});
+
+export const Nothing3: Strategy<State> = strategy("Nothing", function* (state: State) {
+    yield ;
+    return state;
+});
+ 
+
+//// [generatorTypeCheck62.js]
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+function strategy(stratName, gen) {
+    return function* (state) {
+        for (const next of gen(state)) {
+            if (next) {
+                next.lastStrategyApplied = stratName;
+            }
+            yield next;
+        }
+    };
+}
+exports.strategy = strategy;
+exports.Nothing1 = strategy("Nothing", function* (state) {
+    return state;
+});
+exports.Nothing2 = strategy("Nothing", function* (state) {
+    yield state;
+});
+exports.Nothing3 = strategy("Nothing", function* (state) {
+    yield;
+    return state;
+});
diff --git a/tests/baselines/reference/generatorTypeCheck62.symbols b/tests/baselines/reference/generatorTypeCheck62.symbols
new file mode 100644
index 00000000000..580ab208840
--- /dev/null
+++ b/tests/baselines/reference/generatorTypeCheck62.symbols
@@ -0,0 +1,106 @@
+=== tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck62.ts ===
+
+export interface StrategicState {
+>StrategicState : Symbol(StrategicState, Decl(generatorTypeCheck62.ts, 0, 0))
+
+    lastStrategyApplied?: string;
+>lastStrategyApplied : Symbol(StrategicState.lastStrategyApplied, Decl(generatorTypeCheck62.ts, 1, 33))
+}
+
+export function strategy<T extends StrategicState>(stratName: string, gen: (a: T) => IterableIterator<T | undefined>): (a: T) => IterableIterator<T | undefined> {
+>strategy : Symbol(strategy, Decl(generatorTypeCheck62.ts, 3, 1))
+>T : Symbol(T, Decl(generatorTypeCheck62.ts, 5, 25))
+>StrategicState : Symbol(StrategicState, Decl(generatorTypeCheck62.ts, 0, 0))
+>stratName : Symbol(stratName, Decl(generatorTypeCheck62.ts, 5, 51))
+>gen : Symbol(gen, Decl(generatorTypeCheck62.ts, 5, 69))
+>a : Symbol(a, Decl(generatorTypeCheck62.ts, 5, 76))
+>T : Symbol(T, Decl(generatorTypeCheck62.ts, 5, 25))
+>IterableIterator : Symbol(IterableIterator, Decl(lib.es2015.iterable.d.ts, --, --))
+>T : Symbol(T, Decl(generatorTypeCheck62.ts, 5, 25))
+>a : Symbol(a, Decl(generatorTypeCheck62.ts, 5, 120))
+>T : Symbol(T, Decl(generatorTypeCheck62.ts, 5, 25))
+>IterableIterator : Symbol(IterableIterator, Decl(lib.es2015.iterable.d.ts, --, --))
+>T : Symbol(T, Decl(generatorTypeCheck62.ts, 5, 25))
+
+    return function*(state) {
+>state : Symbol(state, Decl(generatorTypeCheck62.ts, 6, 21))
+
+        for (const next of gen(state)) {
+>next : Symbol(next, Decl(generatorTypeCheck62.ts, 7, 18))
+>gen : Symbol(gen, Decl(generatorTypeCheck62.ts, 5, 69))
+>state : Symbol(state, Decl(generatorTypeCheck62.ts, 6, 21))
+
+            if (next) {
+>next : Symbol(next, Decl(generatorTypeCheck62.ts, 7, 18))
+
+                next.lastStrategyApplied = stratName;
+>next.lastStrategyApplied : Symbol(StrategicState.lastStrategyApplied, Decl(generatorTypeCheck62.ts, 1, 33))
+>next : Symbol(next, Decl(generatorTypeCheck62.ts, 7, 18))
+>lastStrategyApplied : Symbol(StrategicState.lastStrategyApplied, Decl(generatorTypeCheck62.ts, 1, 33))
+>stratName : Symbol(stratName, Decl(generatorTypeCheck62.ts, 5, 51))
+            }
+            yield next;
+>next : Symbol(next, Decl(generatorTypeCheck62.ts, 7, 18))
+        }
+    }
+}
+
+export interface Strategy<T> {
+>Strategy : Symbol(Strategy, Decl(generatorTypeCheck62.ts, 14, 1))
+>T : Symbol(T, Decl(generatorTypeCheck62.ts, 16, 26))
+
+    (a: T): IterableIterator<T | undefined>;
+>a : Symbol(a, Decl(generatorTypeCheck62.ts, 17, 5))
+>T : Symbol(T, Decl(generatorTypeCheck62.ts, 16, 26))
+>IterableIterator : Symbol(IterableIterator, Decl(lib.es2015.iterable.d.ts, --, --))
+>T : Symbol(T, Decl(generatorTypeCheck62.ts, 16, 26))
+}
+
+export interface State extends StrategicState {
+>State : Symbol(State, Decl(generatorTypeCheck62.ts, 18, 1))
+>StrategicState : Symbol(StrategicState, Decl(generatorTypeCheck62.ts, 0, 0))
+
+    foo: number;
+>foo : Symbol(State.foo, Decl(generatorTypeCheck62.ts, 20, 47))
+}
+
+export const Nothing1: Strategy<State> = strategy("Nothing", function*(state: State) {
+>Nothing1 : Symbol(Nothing1, Decl(generatorTypeCheck62.ts, 24, 12))
+>Strategy : Symbol(Strategy, Decl(generatorTypeCheck62.ts, 14, 1))
+>State : Symbol(State, Decl(generatorTypeCheck62.ts, 18, 1))
+>strategy : Symbol(strategy, Decl(generatorTypeCheck62.ts, 3, 1))
+>state : Symbol(state, Decl(generatorTypeCheck62.ts, 24, 71))
+>State : Symbol(State, Decl(generatorTypeCheck62.ts, 18, 1))
+
+    return state;
+>state : Symbol(state, Decl(generatorTypeCheck62.ts, 24, 71))
+
+});
+
+export const Nothing2: Strategy<State> = strategy("Nothing", function*(state: State) {
+>Nothing2 : Symbol(Nothing2, Decl(generatorTypeCheck62.ts, 28, 12))
+>Strategy : Symbol(Strategy, Decl(generatorTypeCheck62.ts, 14, 1))
+>State : Symbol(State, Decl(generatorTypeCheck62.ts, 18, 1))
+>strategy : Symbol(strategy, Decl(generatorTypeCheck62.ts, 3, 1))
+>state : Symbol(state, Decl(generatorTypeCheck62.ts, 28, 71))
+>State : Symbol(State, Decl(generatorTypeCheck62.ts, 18, 1))
+
+    yield state;
+>state : Symbol(state, Decl(generatorTypeCheck62.ts, 28, 71))
+
+});
+
+export const Nothing3: Strategy<State> = strategy("Nothing", function* (state: State) {
+>Nothing3 : Symbol(Nothing3, Decl(generatorTypeCheck62.ts, 32, 12))
+>Strategy : Symbol(Strategy, Decl(generatorTypeCheck62.ts, 14, 1))
+>State : Symbol(State, Decl(generatorTypeCheck62.ts, 18, 1))
+>strategy : Symbol(strategy, Decl(generatorTypeCheck62.ts, 3, 1))
+>state : Symbol(state, Decl(generatorTypeCheck62.ts, 32, 72))
+>State : Symbol(State, Decl(generatorTypeCheck62.ts, 18, 1))
+
+    yield ;
+    return state;
+>state : Symbol(state, Decl(generatorTypeCheck62.ts, 32, 72))
+
+});
+ 
diff --git a/tests/baselines/reference/generatorTypeCheck62.types b/tests/baselines/reference/generatorTypeCheck62.types
new file mode 100644
index 00000000000..289d33dc7d4
--- /dev/null
+++ b/tests/baselines/reference/generatorTypeCheck62.types
@@ -0,0 +1,122 @@
+=== tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck62.ts ===
+
+export interface StrategicState {
+>StrategicState : StrategicState
+
+    lastStrategyApplied?: string;
+>lastStrategyApplied : string
+}
+
+export function strategy<T extends StrategicState>(stratName: string, gen: (a: T) => IterableIterator<T | undefined>): (a: T) => IterableIterator<T | undefined> {
+>strategy : <T extends StrategicState>(stratName: string, gen: (a: T) => IterableIterator<T>) => (a: T) => IterableIterator<T>
+>T : T
+>StrategicState : StrategicState
+>stratName : string
+>gen : (a: T) => IterableIterator<T>
+>a : T
+>T : T
+>IterableIterator : IterableIterator<T>
+>T : T
+>a : T
+>T : T
+>IterableIterator : IterableIterator<T>
+>T : T
+
+    return function*(state) {
+>function*(state) {        for (const next of gen(state)) {            if (next) {                next.lastStrategyApplied = stratName;            }            yield next;        }    } : (state: T) => IterableIterator<T>
+>state : T
+
+        for (const next of gen(state)) {
+>next : T
+>gen(state) : IterableIterator<T>
+>gen : (a: T) => IterableIterator<T>
+>state : T
+
+            if (next) {
+>next : T
+
+                next.lastStrategyApplied = stratName;
+>next.lastStrategyApplied = stratName : string
+>next.lastStrategyApplied : string
+>next : T
+>lastStrategyApplied : string
+>stratName : string
+            }
+            yield next;
+>yield next : any
+>next : T
+        }
+    }
+}
+
+export interface Strategy<T> {
+>Strategy : Strategy<T>
+>T : T
+
+    (a: T): IterableIterator<T | undefined>;
+>a : T
+>T : T
+>IterableIterator : IterableIterator<T>
+>T : T
+}
+
+export interface State extends StrategicState {
+>State : State
+>StrategicState : StrategicState
+
+    foo: number;
+>foo : number
+}
+
+export const Nothing1: Strategy<State> = strategy("Nothing", function*(state: State) {
+>Nothing1 : Strategy<State>
+>Strategy : Strategy<T>
+>State : State
+>strategy("Nothing", function*(state: State) {    return state;}) : (a: State) => IterableIterator<State>
+>strategy : <T extends StrategicState>(stratName: string, gen: (a: T) => IterableIterator<T>) => (a: T) => IterableIterator<T>
+>"Nothing" : "Nothing"
+>function*(state: State) {    return state;} : (state: State) => IterableIterator<State>
+>state : State
+>State : State
+
+    return state;
+>state : State
+
+});
+
+export const Nothing2: Strategy<State> = strategy("Nothing", function*(state: State) {
+>Nothing2 : Strategy<State>
+>Strategy : Strategy<T>
+>State : State
+>strategy("Nothing", function*(state: State) {    yield state;}) : (a: State) => IterableIterator<State>
+>strategy : <T extends StrategicState>(stratName: string, gen: (a: T) => IterableIterator<T>) => (a: T) => IterableIterator<T>
+>"Nothing" : "Nothing"
+>function*(state: State) {    yield state;} : (state: State) => IterableIterator<State>
+>state : State
+>State : State
+
+    yield state;
+>yield state : any
+>state : State
+
+});
+
+export const Nothing3: Strategy<State> = strategy("Nothing", function* (state: State) {
+>Nothing3 : Strategy<State>
+>Strategy : Strategy<T>
+>State : State
+>strategy("Nothing", function* (state: State) {    yield ;    return state;}) : (a: State) => IterableIterator<State>
+>strategy : <T extends StrategicState>(stratName: string, gen: (a: T) => IterableIterator<T>) => (a: T) => IterableIterator<T>
+>"Nothing" : "Nothing"
+>function* (state: State) {    yield ;    return state;} : (state: State) => IterableIterator<State>
+>state : State
+>State : State
+
+    yield ;
+>yield : any
+
+    return state;
+>state : State
+
+});
+ 
diff --git a/tests/baselines/reference/generatorTypeCheck63.errors.txt b/tests/baselines/reference/generatorTypeCheck63.errors.txt
new file mode 100644
index 00000000000..46e722a0dd1
--- /dev/null
+++ b/tests/baselines/reference/generatorTypeCheck63.errors.txt
@@ -0,0 +1,63 @@
+tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck63.ts(25,14): error TS2322: Type '(a: State | 1) => IterableIterator<State | 1>' is not assignable to type 'Strategy<State>'.
+  Type 'IterableIterator<State | 1>' is not assignable to type 'IterableIterator<State>'.
+    Type 'State | 1' is not assignable to type 'State'.
+      Type '1' is not assignable to type 'State'.
+tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck63.ts(30,70): error TS7025: Generator implicitly has type 'IterableIterator<any>' because it does not yield any values. Consider supplying a return type.
+tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck63.ts(33,42): error TS2453: The type argument for type parameter 'T' cannot be inferred from the usage. Consider specifying the type arguments explicitly.
+  Type argument candidate 'State' is not a valid type argument because it is not a supertype of candidate '1'.
+tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck63.ts(37,14): error TS2322: Type '(a: State | 1) => IterableIterator<State | 1>' is not assignable to type 'Strategy<State>'.
+
+
+==== tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck63.ts (4 errors) ====
+    
+    export interface StrategicState {
+        lastStrategyApplied?: string;
+    }
+    
+    export function strategy<T extends StrategicState>(stratName: string, gen: (a: T) => IterableIterator<T | undefined>): (a: T) => IterableIterator<T | undefined> {
+        return function*(state) {
+            for (const next of gen(state)) {
+                if (next) {
+                    next.lastStrategyApplied = stratName;
+                }
+                yield next;
+            }
+        }
+    }
+    
+    export interface Strategy<T> {
+        (a: T): IterableIterator<T | undefined>;
+    }
+    
+    export interface State extends StrategicState {
+        foo: number;
+    }
+    
+    export const Nothing: Strategy<State> = strategy("Nothing", function* (state: State) {
+                 ~~~~~~~
+!!! error TS2322: Type '(a: State | 1) => IterableIterator<State | 1>' is not assignable to type 'Strategy<State>'.
+!!! error TS2322:   Type 'IterableIterator<State | 1>' is not assignable to type 'IterableIterator<State>'.
+!!! error TS2322:     Type 'State | 1' is not assignable to type 'State'.
+!!! error TS2322:       Type '1' is not assignable to type 'State'.
+        yield 1;
+        return state;
+    });
+    
+    export const Nothing1: Strategy<State> = strategy("Nothing", function* (state: State) {
+                                                                         ~
+!!! error TS7025: Generator implicitly has type 'IterableIterator<any>' because it does not yield any values. Consider supplying a return type.
+    });
+    
+    export const Nothing2: Strategy<State> = strategy("Nothing", function* (state: State) {
+                                             ~~~~~~~~
+!!! error TS2453: The type argument for type parameter 'T' cannot be inferred from the usage. Consider specifying the type arguments explicitly.
+!!! error TS2453:   Type argument candidate 'State' is not a valid type argument because it is not a supertype of candidate '1'.
+        return 1;
+    });
+    
+    export const Nothing3: Strategy<State> = strategy("Nothing", function* (state: State) {
+                 ~~~~~~~~
+!!! error TS2322: Type '(a: State | 1) => IterableIterator<State | 1>' is not assignable to type 'Strategy<State>'.
+        yield state;
+        return 1;
+    });
\ No newline at end of file
diff --git a/tests/baselines/reference/generatorTypeCheck63.js b/tests/baselines/reference/generatorTypeCheck63.js
new file mode 100644
index 00000000000..92cf2f867fc
--- /dev/null
+++ b/tests/baselines/reference/generatorTypeCheck63.js
@@ -0,0 +1,69 @@
+//// [generatorTypeCheck63.ts]
+
+export interface StrategicState {
+    lastStrategyApplied?: string;
+}
+
+export function strategy<T extends StrategicState>(stratName: string, gen: (a: T) => IterableIterator<T | undefined>): (a: T) => IterableIterator<T | undefined> {
+    return function*(state) {
+        for (const next of gen(state)) {
+            if (next) {
+                next.lastStrategyApplied = stratName;
+            }
+            yield next;
+        }
+    }
+}
+
+export interface Strategy<T> {
+    (a: T): IterableIterator<T | undefined>;
+}
+
+export interface State extends StrategicState {
+    foo: number;
+}
+
+export const Nothing: Strategy<State> = strategy("Nothing", function* (state: State) {
+    yield 1;
+    return state;
+});
+
+export const Nothing1: Strategy<State> = strategy("Nothing", function* (state: State) {
+});
+
+export const Nothing2: Strategy<State> = strategy("Nothing", function* (state: State) {
+    return 1;
+});
+
+export const Nothing3: Strategy<State> = strategy("Nothing", function* (state: State) {
+    yield state;
+    return 1;
+});
+
+//// [generatorTypeCheck63.js]
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+function strategy(stratName, gen) {
+    return function* (state) {
+        for (const next of gen(state)) {
+            if (next) {
+                next.lastStrategyApplied = stratName;
+            }
+            yield next;
+        }
+    };
+}
+exports.strategy = strategy;
+exports.Nothing = strategy("Nothing", function* (state) {
+    yield 1;
+    return state;
+});
+exports.Nothing1 = strategy("Nothing", function* (state) {
+});
+exports.Nothing2 = strategy("Nothing", function* (state) {
+    return 1;
+});
+exports.Nothing3 = strategy("Nothing", function* (state) {
+    yield state;
+    return 1;
+});
diff --git a/tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck62.ts b/tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck62.ts
new file mode 100644
index 00000000000..2f30fe9d902
--- /dev/null
+++ b/tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck62.ts
@@ -0,0 +1,40 @@
+// @module: commonjs
+// @target: es6
+// @noImplicitAny: true
+
+export interface StrategicState {
+    lastStrategyApplied?: string;
+}
+
+export function strategy<T extends StrategicState>(stratName: string, gen: (a: T) => IterableIterator<T | undefined>): (a: T) => IterableIterator<T | undefined> {
+    return function*(state) {
+        for (const next of gen(state)) {
+            if (next) {
+                next.lastStrategyApplied = stratName;
+            }
+            yield next;
+        }
+    }
+}
+
+export interface Strategy<T> {
+    (a: T): IterableIterator<T | undefined>;
+}
+
+export interface State extends StrategicState {
+    foo: number;
+}
+
+export const Nothing1: Strategy<State> = strategy("Nothing", function*(state: State) {
+    return state;
+});
+
+export const Nothing2: Strategy<State> = strategy("Nothing", function*(state: State) {
+    yield state;
+});
+
+export const Nothing3: Strategy<State> = strategy("Nothing", function* (state: State) {
+    yield ;
+    return state;
+});
+ 
\ No newline at end of file
diff --git a/tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck63.ts b/tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck63.ts
new file mode 100644
index 00000000000..58411e409b8
--- /dev/null
+++ b/tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck63.ts
@@ -0,0 +1,43 @@
+// @module: commonjs
+// @target: es6
+// @noImplicitAny: true
+
+export interface StrategicState {
+    lastStrategyApplied?: string;
+}
+
+export function strategy<T extends StrategicState>(stratName: string, gen: (a: T) => IterableIterator<T | undefined>): (a: T) => IterableIterator<T | undefined> {
+    return function*(state) {
+        for (const next of gen(state)) {
+            if (next) {
+                next.lastStrategyApplied = stratName;
+            }
+            yield next;
+        }
+    }
+}
+
+export interface Strategy<T> {
+    (a: T): IterableIterator<T | undefined>;
+}
+
+export interface State extends StrategicState {
+    foo: number;
+}
+
+export const Nothing: Strategy<State> = strategy("Nothing", function* (state: State) {
+    yield 1;
+    return state;
+});
+
+export const Nothing1: Strategy<State> = strategy("Nothing", function* (state: State) {
+});
+
+export const Nothing2: Strategy<State> = strategy("Nothing", function* (state: State) {
+    return 1;
+});
+
+export const Nothing3: Strategy<State> = strategy("Nothing", function* (state: State) {
+    yield state;
+    return 1;
+});
\ No newline at end of file