diff --git a/src/Compilers/CSharp/Portable/Lowering/AsyncRewriter/AsyncMethodBuilderMemberCollection.cs b/src/Compilers/CSharp/Portable/Lowering/AsyncRewriter/AsyncMethodBuilderMemberCollection.cs
index 18b3675cf21ad..f95c9c6d93afd 100644
--- a/src/Compilers/CSharp/Portable/Lowering/AsyncRewriter/AsyncMethodBuilderMemberCollection.cs
+++ b/src/Compilers/CSharp/Portable/Lowering/AsyncRewriter/AsyncMethodBuilderMemberCollection.cs
@@ -250,8 +250,14 @@ private static bool TryCreate(
                 TryGetWellKnownMethodAsMember(F, awaitOnCompleted, builderType, requireWellKnownType, out awaitOnCompletedMethod) &&
                 TryGetWellKnownMethodAsMember(F, awaitUnsafeOnCompleted, builderType, requireWellKnownType, out awaitUnsafeOnCompletedMethod) &&
                 TryGetWellKnownMethodAsMember(F, start, builderType, requireWellKnownType, out startMethod) &&
-                TryGetWellKnownMethodAsMember(F, setStateMachine, builderType, requireWellKnownType, out setStateMachineMethod))
+                TryGetWellKnownMethodAsMember(F, setStateMachine, builderType, requireWellKnownType, out setStateMachineMethod) &&
+                HasOnlyConstraint(F, startMethod.TypeParameters[0], WellKnownType.System_Runtime_CompilerServices_IAsyncStateMachine) &&
+                HasOnlyConstraint(F, awaitOnCompletedMethod.TypeParameters[0], WellKnownType.System_Runtime_CompilerServices_INotifyCompletion) &&
+                HasOnlyConstraint(F, awaitOnCompletedMethod.TypeParameters[1], WellKnownType.System_Runtime_CompilerServices_IAsyncStateMachine) &&
+                HasOnlyConstraint(F, awaitUnsafeOnCompletedMethod.TypeParameters[0], WellKnownType.System_Runtime_CompilerServices_ICriticalNotifyCompletion) &&
+                HasOnlyConstraint(F, awaitUnsafeOnCompletedMethod.TypeParameters[1], WellKnownType.System_Runtime_CompilerServices_IAsyncStateMachine))
             {
+
                 collection = new AsyncMethodBuilderMemberCollection(
                     builderType,
                     resultType,
@@ -270,6 +276,22 @@ private static bool TryCreate(
             return false;
         }
 
+        private static bool HasOnlyConstraint(SyntheticBoundNodeFactory F, TypeParameterSymbol typeParameter, WellKnownType constraint)
+        {
+            if (!typeParameter.HasConstructorConstraint &&
+                !typeParameter.HasValueTypeConstraint &&
+                !typeParameter.HasReferenceTypeConstraint &&
+                typeParameter.ConstraintTypes.Length == 1 &&
+                typeParameter.ConstraintTypes[0] == F.WellKnownType(constraint))
+            {
+                return true;
+            }
+
+            object[] args = new object[] { typeParameter.MetadataName, F.WellKnownType(constraint).MetadataName };
+            CSDiagnostic error = new CSDiagnostic(new CSDiagnosticInfo(ErrorCode.ERR_MissingPredefinedMember, args), F.Syntax.Location, false);
+            throw new SyntheticBoundNodeFactory.MissingPredefinedMember(error);
+        }
+
         private static bool TryGetWellKnownMethodAsMember(SyntheticBoundNodeFactory F, WellKnownMember wellKnownMethod, NamedTypeSymbol containingType, bool requireWellKnownType, out MethodSymbol methodSymbol)
         {
             if (requireWellKnownType)
diff --git a/src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenAsyncTests.cs b/src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenAsyncTests.cs
index 303e50931b3fa..8508a20fc96cf 100644
--- a/src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenAsyncTests.cs
+++ b/src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenAsyncTests.cs
@@ -3375,6 +3375,83 @@ namespace System.Runtime.CompilerServices { class TasklikeAttribute : Attribute
                 );
         }
 
+        [Fact]
+        public void AsyncTasklikeBuilderConstraints()
+        {
+            var source1 = @"
+using System;
+using System.Runtime.CompilerServices;
+using System.Threading.Tasks;
+class C
+{
+    static void Main() { }
+    async MyTask f() { await (Task)null; }
+}
+
+[Tasklike(typeof(MyTaskBuilder))]
+class MyTask { }
+
+interface I { }
+
+class MyTaskBuilder
+{
+    public static MyTaskBuilder Create() => null;
+    public void SetStateMachine(IAsyncStateMachine stateMachine) { }
+    public void Start<TSM>(ref TSM stateMachine) where TSM : I { }
+    public void AwaitOnCompleted<TA, TSM>(ref TA awaiter, ref TSM stateMachine) { }
+    public void AwaitUnsafeOnCompleted<TA, TSM>(ref TA awaiter, ref TSM stateMachine) { }
+    public void SetResult() { }
+    public void SetException(Exception ex) { }
+    public MyTask Task => null;
+}
+
+namespace System.Runtime.CompilerServices { public class TasklikeAttribute : Attribute { public TasklikeAttribute(Type builder) { } } }
+";
+
+            var comp1 = CreateCompilation(source1, options: TestOptions.DebugExe);
+            comp1.VerifyEmitDiagnostics(
+                // (8,22): error CS0656: Missing compiler required member 'TSM.IAsyncStateMachine'
+                //     async MyTask f() { await (Task)null; }
+                Diagnostic(ErrorCode.ERR_MissingPredefinedMember, "{ await (Task)null; }").WithArguments("TSM", "IAsyncStateMachine").WithLocation(8, 22)
+                );
+
+            var source2 = @"
+using System;
+using System.Runtime.CompilerServices;
+using System.Threading.Tasks;
+class C
+{
+    static void Main() { }
+    async MyTask f() { await (Task)null; }
+}
+
+[Tasklike(typeof(MyTaskBuilder))]
+class MyTask { }
+
+class MyTaskBuilder
+{
+    public static MyTaskBuilder Create() => null;
+    public void SetStateMachine(IAsyncStateMachine stateMachine) { }
+    public void Start<TSM>(ref TSM stateMachine) where TSM : IAsyncStateMachine { }
+    public void AwaitOnCompleted<TA, TSM>(ref TA awaiter, ref TSM stateMachine) where TA : INotifyCompletion where TSM : IAsyncStateMachine { }
+    public void AwaitUnsafeOnCompleted<TA, TSM>(ref TA awaiter, ref TSM stateMachine) { }
+    public void SetResult() { }
+    public void SetException(Exception ex) { }
+    public MyTask Task => null;
+}
+
+namespace System.Runtime.CompilerServices { public class TasklikeAttribute : Attribute { public TasklikeAttribute(Type builder) { } } }
+";
+
+            var comp2 = CreateCompilation(source2, options: TestOptions.DebugExe);
+            comp2.VerifyEmitDiagnostics(
+                // (8,22): error CS0656: Missing compiler required member 'TA.ICriticalNotifyCompletion'
+                //     async MyTask f() { await (Task)null; }
+                Diagnostic(ErrorCode.ERR_MissingPredefinedMember, "{ await (Task)null; }").WithArguments("TA", "ICriticalNotifyCompletion").WithLocation(8, 22)
+                );
+
+        }
+
 
 
         [Fact]