diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 903c8cfda1c20..cc498cfe4d8b6 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -16199,7 +16199,7 @@ namespace ts {
                 return undefined;
             }
 
-            const onfulfilledParameterType = getTypeWithFacts(getUnionType(map(thenSignatures, getTypeOfFirstParameterOfSignature)), TypeFacts.NEUndefined);
+            const onfulfilledParameterType = getTypeWithFacts(getUnionType(map(thenSignatures, getTypeOfFirstParameterOfSignature)), TypeFacts.NEUndefinedOrNull);
             if (isTypeAny(onfulfilledParameterType)) {
                 return undefined;
             }
diff --git a/src/compiler/transformers/ts.ts b/src/compiler/transformers/ts.ts
index 749ea46c8f20c..77af854269e33 100644
--- a/src/compiler/transformers/ts.ts
+++ b/src/compiler/transformers/ts.ts
@@ -1223,11 +1223,12 @@ namespace ts {
             }
 
             const { firstAccessor, secondAccessor, setAccessor } = getAllAccessorDeclarations(node.members, accessor);
-            if (accessor !== firstAccessor) {
+            const firstAccessorWithDecorators = firstAccessor.decorators ? firstAccessor : secondAccessor && secondAccessor.decorators ? secondAccessor : undefined;
+            if (!firstAccessorWithDecorators || accessor !== firstAccessorWithDecorators) {
                 return undefined;
             }
 
-            const decorators = firstAccessor.decorators || (secondAccessor && secondAccessor.decorators);
+            const decorators = firstAccessorWithDecorators.decorators;
             const parameters = getDecoratorsOfParameters(setAccessor);
             if (!decorators && !parameters) {
                 return undefined;
diff --git a/tests/baselines/reference/awaitInheritedPromise_es2017.js b/tests/baselines/reference/awaitInheritedPromise_es2017.js
new file mode 100644
index 0000000000000..e973d0b166aeb
--- /dev/null
+++ b/tests/baselines/reference/awaitInheritedPromise_es2017.js
@@ -0,0 +1,11 @@
+//// [awaitInheritedPromise_es2017.ts]
+interface A extends Promise<string> {}
+declare var a: A;
+async function f() {
+    await a;
+}
+
+//// [awaitInheritedPromise_es2017.js]
+async function f() {
+    await a;
+}
diff --git a/tests/baselines/reference/awaitInheritedPromise_es2017.symbols b/tests/baselines/reference/awaitInheritedPromise_es2017.symbols
new file mode 100644
index 0000000000000..ef68d16b67818
--- /dev/null
+++ b/tests/baselines/reference/awaitInheritedPromise_es2017.symbols
@@ -0,0 +1,15 @@
+=== tests/cases/conformance/async/es2017/awaitInheritedPromise_es2017.ts ===
+interface A extends Promise<string> {}
+>A : Symbol(A, Decl(awaitInheritedPromise_es2017.ts, 0, 0))
+>Promise : Symbol(Promise, Decl(lib.es2015.symbol.wellknown.d.ts, --, --), Decl(lib.es2015.promise.d.ts, --, --), Decl(lib.es2015.promise.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --))
+
+declare var a: A;
+>a : Symbol(a, Decl(awaitInheritedPromise_es2017.ts, 1, 11))
+>A : Symbol(A, Decl(awaitInheritedPromise_es2017.ts, 0, 0))
+
+async function f() {
+>f : Symbol(f, Decl(awaitInheritedPromise_es2017.ts, 1, 17))
+
+    await a;
+>a : Symbol(a, Decl(awaitInheritedPromise_es2017.ts, 1, 11))
+}
diff --git a/tests/baselines/reference/awaitInheritedPromise_es2017.types b/tests/baselines/reference/awaitInheritedPromise_es2017.types
new file mode 100644
index 0000000000000..bed681181b0b7
--- /dev/null
+++ b/tests/baselines/reference/awaitInheritedPromise_es2017.types
@@ -0,0 +1,16 @@
+=== tests/cases/conformance/async/es2017/awaitInheritedPromise_es2017.ts ===
+interface A extends Promise<string> {}
+>A : A
+>Promise : Promise<T>
+
+declare var a: A;
+>a : A
+>A : A
+
+async function f() {
+>f : () => Promise<void>
+
+    await a;
+>await a : string
+>a : A
+}
diff --git a/tests/baselines/reference/decoratorOnClassAccessor7.errors.txt b/tests/baselines/reference/decoratorOnClassAccessor7.errors.txt
new file mode 100644
index 0000000000000..d776297fcf461
--- /dev/null
+++ b/tests/baselines/reference/decoratorOnClassAccessor7.errors.txt
@@ -0,0 +1,41 @@
+tests/cases/conformance/decorators/class/accessor/decoratorOnClassAccessor7.ts(26,5): error TS1207: Decorators cannot be applied to multiple get/set accessors of the same name.
+tests/cases/conformance/decorators/class/accessor/decoratorOnClassAccessor7.ts(31,5): error TS1207: Decorators cannot be applied to multiple get/set accessors of the same name.
+
+
+==== tests/cases/conformance/decorators/class/accessor/decoratorOnClassAccessor7.ts (2 errors) ====
+    declare function dec1<T>(target: any, propertyKey: string, descriptor: TypedPropertyDescriptor<T>): TypedPropertyDescriptor<T>;
+    declare function dec2<T>(target: any, propertyKey: string, descriptor: TypedPropertyDescriptor<T>): TypedPropertyDescriptor<T>;
+    
+    class A {
+        @dec1 get x() { return 0; }
+        set x(value: number) { }
+    }
+    
+    class B {
+        get x() { return 0; }
+        @dec2 set x(value: number) { }
+    }
+    
+    class C {
+        @dec1 set x(value: number) { }
+        get x() { return 0; }
+    }
+    
+    class D {
+        set x(value: number) { }
+        @dec2 get x() { return 0; }
+    }
+    
+    class E {
+        @dec1 get x() { return 0; }
+        @dec2 set x(value: number) { }
+        ~
+!!! error TS1207: Decorators cannot be applied to multiple get/set accessors of the same name.
+    }
+    
+    class F {
+        @dec1 set x(value: number) { }
+        @dec2 get x() { return 0; }
+        ~
+!!! error TS1207: Decorators cannot be applied to multiple get/set accessors of the same name.
+    }
\ No newline at end of file
diff --git a/tests/baselines/reference/decoratorOnClassAccessor7.js b/tests/baselines/reference/decoratorOnClassAccessor7.js
new file mode 100644
index 0000000000000..5ae0c29c14b38
--- /dev/null
+++ b/tests/baselines/reference/decoratorOnClassAccessor7.js
@@ -0,0 +1,125 @@
+//// [decoratorOnClassAccessor7.ts]
+declare function dec1<T>(target: any, propertyKey: string, descriptor: TypedPropertyDescriptor<T>): TypedPropertyDescriptor<T>;
+declare function dec2<T>(target: any, propertyKey: string, descriptor: TypedPropertyDescriptor<T>): TypedPropertyDescriptor<T>;
+
+class A {
+    @dec1 get x() { return 0; }
+    set x(value: number) { }
+}
+
+class B {
+    get x() { return 0; }
+    @dec2 set x(value: number) { }
+}
+
+class C {
+    @dec1 set x(value: number) { }
+    get x() { return 0; }
+}
+
+class D {
+    set x(value: number) { }
+    @dec2 get x() { return 0; }
+}
+
+class E {
+    @dec1 get x() { return 0; }
+    @dec2 set x(value: number) { }
+}
+
+class F {
+    @dec1 set x(value: number) { }
+    @dec2 get x() { return 0; }
+}
+
+//// [decoratorOnClassAccessor7.js]
+var __decorate = (this && this.__decorate) || function (decorators, target, key, desc) {
+    var c = arguments.length, r = c < 3 ? target : desc === null ? desc = Object.getOwnPropertyDescriptor(target, key) : desc, d;
+    if (typeof Reflect === "object" && typeof Reflect.decorate === "function") r = Reflect.decorate(decorators, target, key, desc);
+    else for (var i = decorators.length - 1; i >= 0; i--) if (d = decorators[i]) r = (c < 3 ? d(r) : c > 3 ? d(target, key, r) : d(target, key)) || r;
+    return c > 3 && r && Object.defineProperty(target, key, r), r;
+};
+var A = (function () {
+    function A() {
+    }
+    Object.defineProperty(A.prototype, "x", {
+        get: function () { return 0; },
+        set: function (value) { },
+        enumerable: true,
+        configurable: true
+    });
+    return A;
+}());
+__decorate([
+    dec1
+], A.prototype, "x", null);
+var B = (function () {
+    function B() {
+    }
+    Object.defineProperty(B.prototype, "x", {
+        get: function () { return 0; },
+        set: function (value) { },
+        enumerable: true,
+        configurable: true
+    });
+    return B;
+}());
+__decorate([
+    dec2
+], B.prototype, "x", null);
+var C = (function () {
+    function C() {
+    }
+    Object.defineProperty(C.prototype, "x", {
+        get: function () { return 0; },
+        set: function (value) { },
+        enumerable: true,
+        configurable: true
+    });
+    return C;
+}());
+__decorate([
+    dec1
+], C.prototype, "x", null);
+var D = (function () {
+    function D() {
+    }
+    Object.defineProperty(D.prototype, "x", {
+        get: function () { return 0; },
+        set: function (value) { },
+        enumerable: true,
+        configurable: true
+    });
+    return D;
+}());
+__decorate([
+    dec2
+], D.prototype, "x", null);
+var E = (function () {
+    function E() {
+    }
+    Object.defineProperty(E.prototype, "x", {
+        get: function () { return 0; },
+        set: function (value) { },
+        enumerable: true,
+        configurable: true
+    });
+    return E;
+}());
+__decorate([
+    dec1
+], E.prototype, "x", null);
+var F = (function () {
+    function F() {
+    }
+    Object.defineProperty(F.prototype, "x", {
+        get: function () { return 0; },
+        set: function (value) { },
+        enumerable: true,
+        configurable: true
+    });
+    return F;
+}());
+__decorate([
+    dec1
+], F.prototype, "x", null);
diff --git a/tests/cases/conformance/async/es2017/awaitInheritedPromise_es2017.ts b/tests/cases/conformance/async/es2017/awaitInheritedPromise_es2017.ts
new file mode 100644
index 0000000000000..c5cd486e0f0d8
--- /dev/null
+++ b/tests/cases/conformance/async/es2017/awaitInheritedPromise_es2017.ts
@@ -0,0 +1,7 @@
+// @target: es2017
+// @strictNullChecks: true
+interface A extends Promise<string> {}
+declare var a: A;
+async function f() {
+    await a;
+}
\ No newline at end of file
diff --git a/tests/cases/conformance/decorators/class/accessor/decoratorOnClassAccessor7.ts b/tests/cases/conformance/decorators/class/accessor/decoratorOnClassAccessor7.ts
new file mode 100644
index 0000000000000..b20a5a85dfbf8
--- /dev/null
+++ b/tests/cases/conformance/decorators/class/accessor/decoratorOnClassAccessor7.ts
@@ -0,0 +1,34 @@
+// @target:es5
+// @experimentaldecorators: true
+declare function dec1<T>(target: any, propertyKey: string, descriptor: TypedPropertyDescriptor<T>): TypedPropertyDescriptor<T>;
+declare function dec2<T>(target: any, propertyKey: string, descriptor: TypedPropertyDescriptor<T>): TypedPropertyDescriptor<T>;
+
+class A {
+    @dec1 get x() { return 0; }
+    set x(value: number) { }
+}
+
+class B {
+    get x() { return 0; }
+    @dec2 set x(value: number) { }
+}
+
+class C {
+    @dec1 set x(value: number) { }
+    get x() { return 0; }
+}
+
+class D {
+    set x(value: number) { }
+    @dec2 get x() { return 0; }
+}
+
+class E {
+    @dec1 get x() { return 0; }
+    @dec2 set x(value: number) { }
+}
+
+class F {
+    @dec1 set x(value: number) { }
+    @dec2 get x() { return 0; }
+}
\ No newline at end of file