diff --git a/pkg/_fe_analyzer_shared/test/inheritance/data/infer_parameter_opt_in.dart b/pkg/_fe_analyzer_shared/test/inheritance/data/infer_parameter_opt_in.dart
index ce6524550cd..0ee78c73e7f 100644
--- a/pkg/_fe_analyzer_shared/test/inheritance/data/infer_parameter_opt_in.dart
+++ b/pkg/_fe_analyzer_shared/test/inheritance/data/infer_parameter_opt_in.dart
@@ -56,57 +56,49 @@ class E4 implements B, A {
 
 /*class: F1:A,C,F1,Object*/
 class F1 extends A implements C {
-  /*cfe|cfe:builder.member: F1.method:void Function(void, {void named})*/
-  /*analyzer.member: F1.method:Object? Function(Object?, {Object? named})*/
+  /*member: F1.method:Object? Function(Object?, {Object? named})*/
   method(o, {named}) {}
 }
 
 /*class: F2:A,C,F2,Object*/
 class F2 extends C implements A {
-  /*cfe|cfe:builder.member: F2.method:void Function(void, {void named})*/
-  /*analyzer.member: F2.method:Object? Function(Object?, {Object? named})*/
+  /*member: F2.method:Object? Function(Object?, {Object? named})*/
   method(o, {named}) {}
 }
 
 /*class: F3:A,C,F3,Object*/
 class F3 implements A, C {
-  /*cfe|cfe:builder.member: F3.method:void Function(void, {void named})*/
-  /*analyzer.member: F3.method:Object? Function(Object?, {Object? named})*/
+  /*member: F3.method:Object? Function(Object?, {Object? named})*/
   method(o, {named}) {}
 }
 
 /*class: F4:A,C,F4,Object*/
 class F4 implements C, A {
-  /*cfe|cfe:builder.member: F4.method:void Function(void, {void named})*/
-  /*analyzer.member: F4.method:Object? Function(Object?, {Object? named})*/
+  /*member: F4.method:Object? Function(Object?, {Object? named})*/
   method(o, {named}) {}
 }
 
 /*class: G1:A,B,C,G1,Object*/
 class G1 extends B implements C {
-  /*cfe|cfe:builder.member: G1.method:void Function(void, {void named})*/
-  /*analyzer.member: G1.method:Object? Function(Object?, {Object? named})*/
+  /*member: G1.method:Object? Function(Object?, {Object? named})*/
   method(o, {named}) {}
 }
 
 /*class: G2:A,B,C,G2,Object*/
 class G2 extends C implements B {
-  /*cfe|cfe:builder.member: G2.method:void Function(void, {void named})*/
-  /*analyzer.member: G2.method:Object? Function(Object?, {Object? named})*/
+  /*member: G2.method:Object? Function(Object?, {Object? named})*/
   method(o, {named}) {}
 }
 
 /*class: G3:A,B,C,G3,Object*/
 class G3 implements B, C {
-  /*cfe|cfe:builder.member: G3.method:void Function(void, {void named})*/
-  /*analyzer.member: G3.method:Object? Function(Object?, {Object? named})*/
+  /*member: G3.method:Object? Function(Object?, {Object? named})*/
   method(o, {named}) {}
 }
 
 /*class: G4:A,B,C,G4,Object*/
 class G4 implements C, B {
-  /*cfe|cfe:builder.member: G4.method:void Function(void, {void named})*/
-  /*analyzer.member: G4.method:Object? Function(Object?, {Object? named})*/
+  /*member: G4.method:Object? Function(Object?, {Object? named})*/
   method(o, {named}) {}
 }
 
diff --git a/pkg/_fe_analyzer_shared/test/inheritance/data/issue40481.dart b/pkg/_fe_analyzer_shared/test/inheritance/data/issue40481.dart
index a388a8d1320..5b562498dab 100644
--- a/pkg/_fe_analyzer_shared/test/inheritance/data/issue40481.dart
+++ b/pkg/_fe_analyzer_shared/test/inheritance/data/issue40481.dart
@@ -19,8 +19,7 @@ class A_void implements A<void> {}
 /*class: B1:A<Object?>,A_Object,A_dynamic,B1,Object*/
 class B1 extends A_Object implements A_dynamic {}
 
-/*cfe|cfe:builder.class: B2:A<void>,A_Object,A_void,B2,Object*/
-/*analyzer.class: B2:A<Object?>,A_Object,A_void,B2,Object*/
+/*class: B2:A<Object?>,A_Object,A_void,B2,Object*/
 class B2 extends A_Object implements A_void {}
 
 main() {}
diff --git a/pkg/_fe_analyzer_shared/test/inheritance/data/issue40481/main.dart b/pkg/_fe_analyzer_shared/test/inheritance/data/issue40481/main.dart
index a84f5d184af..64689932a84 100644
--- a/pkg/_fe_analyzer_shared/test/inheritance/data/issue40481/main.dart
+++ b/pkg/_fe_analyzer_shared/test/inheritance/data/issue40481/main.dart
@@ -15,8 +15,7 @@ class A_void implements A<void> {}
 /*class: B1:A<Object?>,A_Object,A_dynamic,B1,Object*/
 class B1 extends A_Object implements A_dynamic {}
 
-/*cfe|cfe:builder.class: B2:A<void>,A_Object,A_void,B2,Object*/
-/*analyzer.class: B2:A<Object?>,A_Object,A_void,B2,Object*/
+/*class: B2:A<Object?>,A_Object,A_void,B2,Object*/
 class B2 extends A_Object implements A_void {}
 
 main() {}
diff --git a/pkg/_fe_analyzer_shared/test/inheritance/data/top_merge_direct.dart b/pkg/_fe_analyzer_shared/test/inheritance/data/top_merge_direct.dart
new file mode 100644
index 00000000000..bb1b4ab637e
--- /dev/null
+++ b/pkg/_fe_analyzer_shared/test/inheritance/data/top_merge_direct.dart
@@ -0,0 +1,47 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/*library: nnbd=true*/
+
+/*class: A:A<T>,Object*/
+class A<T> {
+  /*member: A.member:T Function()*/
+  T member() => throw "Unreachable";
+}
+
+/*class: B:A<T>,B<T>,Object*/
+/*member: B.member:T Function()*/
+class B<T> extends A<T> {}
+
+/*class: D0:A<Object?>,B<Object?>,D0,Object*/
+/*member: D0.member:Object? Function()*/
+class D0 extends A<dynamic> implements B<Object?> {}
+
+/*class: D1:A<Object?>,B<dynamic>,D1,Object*/
+/*member: D1.member:Object? Function()*/
+class D1 extends A<Object?> implements B<dynamic> {}
+
+/*class: D2:A<Object?>,B<Object?>,D2,Object*/
+/*member: D2.member:Object? Function()*/
+class D2 extends A<void> implements B<Object?> {}
+
+/*class: D3:A<Object?>,B<void>,D3,Object*/
+/*member: D3.member:Object? Function()*/
+class D3 extends A<Object?> implements B<void> {}
+
+/*class: D4:A<Object?>,B<dynamic>,D4,Object*/
+/*member: D4.member:Object? Function()*/
+class D4 extends A<void> implements B<dynamic> {}
+
+/*class: D5:A<Object?>,B<void>,D5,Object*/
+/*member: D5.member:Object? Function()*/
+class D5 extends A<dynamic> implements B<void> {}
+
+/*class: D6:A<void>,B<void>,D6,Object*/
+/*member: D6.member:void Function()*/
+class D6 extends A<void> implements B<void> {}
+
+/*class: D7:A<dynamic>,B<dynamic>,D7,Object*/
+/*member: D7.member:dynamic Function()*/
+class D7 extends A<dynamic> implements B<dynamic> {}
diff --git a/pkg/_fe_analyzer_shared/test/inheritance/data/top_merge_mixin.dart b/pkg/_fe_analyzer_shared/test/inheritance/data/top_merge_mixin.dart
new file mode 100644
index 00000000000..597a802b8ab
--- /dev/null
+++ b/pkg/_fe_analyzer_shared/test/inheritance/data/top_merge_mixin.dart
@@ -0,0 +1,49 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/*library: nnbd=true*/
+
+/*class: A:A<T>,Object*/
+abstract class A<T> {
+  /*member: A.member:T Function()*/
+  T member();
+}
+
+/*cfe|cfe:builder.class: B:B<T>,Object*/
+/*cfe|cfe:builder.member: B.member:T Function()*/
+mixin B<T> {
+  T member();
+}
+
+/*class: D0:A<dynamic>,B<Object?>,D0,Object*/
+/*member: D0.member:Object? Function()*/
+abstract class D0 extends A<dynamic> with B<Object?> {}
+
+/*class: D1:A<Object?>,B<dynamic>,D1,Object*/
+/*member: D1.member:dynamic Function()*/
+abstract class D1 extends A<Object?> with B<dynamic> {}
+
+/*class: D2:A<void>,B<Object?>,D2,Object*/
+/*member: D2.member:Object? Function()*/
+abstract class D2 extends A<void> with B<Object?> {}
+
+/*class: D3:A<Object?>,B<void>,D3,Object*/
+/*member: D3.member:void Function()*/
+abstract class D3 extends A<Object?> with B<void> {}
+
+/*class: D4:A<void>,B<dynamic>,D4,Object*/
+/*member: D4.member:dynamic Function()*/
+abstract class D4 extends A<void> with B<dynamic> {}
+
+/*class: D5:A<dynamic>,B<void>,D5,Object*/
+/*member: D5.member:void Function()*/
+abstract class D5 extends A<dynamic> with B<void> {}
+
+/*class: D6:A<void>,B<void>,D6,Object*/
+/*member: D6.member:void Function()*/
+abstract class D6 extends A<void> with B<void> {}
+
+/*class: D7:A<dynamic>,B<dynamic>,D7,Object*/
+/*member: D7.member:dynamic Function()*/
+abstract class D7 extends A<dynamic> with B<dynamic> {}
diff --git a/pkg/_fe_analyzer_shared/test/inheritance/data/top_merge_opt_in.dart b/pkg/_fe_analyzer_shared/test/inheritance/data/top_merge_opt_in.dart
index bd4dc1f0e52..3845f870d4d 100644
--- a/pkg/_fe_analyzer_shared/test/inheritance/data/top_merge_opt_in.dart
+++ b/pkg/_fe_analyzer_shared/test/inheritance/data/top_merge_opt_in.dart
@@ -32,8 +32,7 @@ abstract class D {
 
 /*class: E1:A,B,C,D,E1,Object*/
 abstract class E1 implements A, B, C, D {
-  /*cfe|cfe:builder.member: E1.method:void Function(void)*/
-  /*analyzer.member: E1.method:Object? Function(Object?)*/
+  /*member: E1.method:Object? Function(Object?)*/
 }
 
 /*class: E2:A,B,E2,Object*/
@@ -43,14 +42,12 @@ abstract class E2 implements A, B {
 
 /*class: E3:B,C,E3,Object*/
 abstract class E3 implements B, C {
-  /*cfe|cfe:builder.member: E3.method:void Function(void)*/
-  /*analyzer.member: E3.method:Object? Function(Object?)*/
+  /*member: E3.method:Object? Function(Object?)*/
 }
 
 /*class: E4:A,C,E4,Object*/
 abstract class E4 implements A, C {
-  /*cfe|cfe:builder.member: E4.method:void Function(void)*/
-  /*analyzer.member: E4.method:Object? Function(Object?)*/
+  /*member: E4.method:Object? Function(Object?)*/
 }
 
 /*class: E5:A,D,E5,Object*/
@@ -71,24 +68,20 @@ abstract class F {
 
 /*class: G1:A,C,F,G1,Object*/
 abstract class G1 implements A, C, F {
-  /*cfe|cfe:builder.member: G1.method:void Function(void)*/
-  /*analyzer.member: G1.method:Object? Function(Object?)*/
+  /*member: G1.method:Object? Function(Object?)*/
 }
 
 /*class: G2:A,C,F,G2,Object*/
 abstract class G2 implements A, F, C {
-  /*cfe|cfe:builder.member: G2.method:void Function(void)*/
-  /*analyzer.member: G2.method:Object? Function(Object?)*/
+  /*member: G2.method:Object? Function(Object?)*/
 }
 
 /*class: G3:A,C,F,G3,Object*/
 abstract class G3 implements C, A, F {
-  /*cfe|cfe:builder.member: G3.method:void Function(void)*/
-  /*analyzer.member: G3.method:Object? Function(Object?)*/
+  /*member: G3.method:Object? Function(Object?)*/
 }
 
 /*class: G4:A,C,F,G4,Object*/
 abstract class G4 implements C, F, A {
-  /*cfe|cfe:builder.member: G4.method:void Function(void)*/
-  /*analyzer.member: G4.method:Object? Function(Object?)*/
+  /*member: G4.method:Object? Function(Object?)*/
 }
diff --git a/pkg/front_end/testcases/nnbd/infer_method_types.dart.outline.expect b/pkg/front_end/testcases/nnbd/infer_method_types.dart.outline.expect
index 5f8c4b8f1e7..f0f39bc4674 100644
--- a/pkg/front_end/testcases/nnbd/infer_method_types.dart.outline.expect
+++ b/pkg/front_end/testcases/nnbd/infer_method_types.dart.outline.expect
@@ -40,7 +40,7 @@ abstract class G extends core::Object implements self::C {
 abstract class H extends core::Object implements self::D, self::E, self::F, self::C {
   synthetic constructor •() → self::H
     ;
-  abstract forwarding-stub member-signature method m(covariant core::num a) → void;
+  abstract forwarding-stub member-signature method m(covariant core::num a) → core::Object?;
 }
 abstract class I extends core::Object implements self::D {
   synthetic constructor •() → self::I
@@ -50,17 +50,17 @@ abstract class I extends core::Object implements self::D {
 abstract class J extends core::Object implements self::H {
   synthetic constructor •() → self::J
     ;
-  abstract method m(covariant core::num a) → void;
+  abstract method m(covariant core::num a) → core::Object?;
 }
 abstract class K extends core::Object implements self::I, self::E, self::G {
   synthetic constructor •() → self::K
     ;
-  abstract forwarding-stub member-signature method m(covariant core::num a) → void;
+  abstract forwarding-stub member-signature method m(covariant core::num a) → core::Object?;
 }
 abstract class L extends core::Object implements self::K {
   synthetic constructor •() → self::L
     ;
-  abstract method m(covariant core::num a) → void;
+  abstract method m(covariant core::num a) → core::Object?;
 }
 static method main() → dynamic
   ;
diff --git a/pkg/front_end/testcases/nnbd/infer_method_types.dart.strong.expect b/pkg/front_end/testcases/nnbd/infer_method_types.dart.strong.expect
index cc03fc1a27c..85e72a08854 100644
--- a/pkg/front_end/testcases/nnbd/infer_method_types.dart.strong.expect
+++ b/pkg/front_end/testcases/nnbd/infer_method_types.dart.strong.expect
@@ -48,7 +48,7 @@ abstract class H extends core::Object implements self::D, self::E, self::F, self
   synthetic constructor •() → self::H
     : super core::Object::•()
     ;
-  abstract forwarding-stub member-signature method m(covariant core::num a) → void;
+  abstract forwarding-stub member-signature method m(covariant core::num a) → core::Object?;
 }
 abstract class I extends core::Object implements self::D {
   synthetic constructor •() → self::I
@@ -60,18 +60,18 @@ abstract class J extends core::Object implements self::H {
   synthetic constructor •() → self::J
     : super core::Object::•()
     ;
-  abstract method m(covariant core::num a) → void;
+  abstract method m(covariant core::num a) → core::Object?;
 }
 abstract class K extends core::Object implements self::I, self::E, self::G {
   synthetic constructor •() → self::K
     : super core::Object::•()
     ;
-  abstract forwarding-stub member-signature method m(covariant core::num a) → void;
+  abstract forwarding-stub member-signature method m(covariant core::num a) → core::Object?;
 }
 abstract class L extends core::Object implements self::K {
   synthetic constructor •() → self::L
     : super core::Object::•()
     ;
-  abstract method m(covariant core::num a) → void;
+  abstract method m(covariant core::num a) → core::Object?;
 }
 static method main() → dynamic {}
diff --git a/pkg/front_end/testcases/nnbd/infer_method_types.dart.strong.transformed.expect b/pkg/front_end/testcases/nnbd/infer_method_types.dart.strong.transformed.expect
index cc03fc1a27c..85e72a08854 100644
--- a/pkg/front_end/testcases/nnbd/infer_method_types.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/infer_method_types.dart.strong.transformed.expect
@@ -48,7 +48,7 @@ abstract class H extends core::Object implements self::D, self::E, self::F, self
   synthetic constructor •() → self::H
     : super core::Object::•()
     ;
-  abstract forwarding-stub member-signature method m(covariant core::num a) → void;
+  abstract forwarding-stub member-signature method m(covariant core::num a) → core::Object?;
 }
 abstract class I extends core::Object implements self::D {
   synthetic constructor •() → self::I
@@ -60,18 +60,18 @@ abstract class J extends core::Object implements self::H {
   synthetic constructor •() → self::J
     : super core::Object::•()
     ;
-  abstract method m(covariant core::num a) → void;
+  abstract method m(covariant core::num a) → core::Object?;
 }
 abstract class K extends core::Object implements self::I, self::E, self::G {
   synthetic constructor •() → self::K
     : super core::Object::•()
     ;
-  abstract forwarding-stub member-signature method m(covariant core::num a) → void;
+  abstract forwarding-stub member-signature method m(covariant core::num a) → core::Object?;
 }
 abstract class L extends core::Object implements self::K {
   synthetic constructor •() → self::L
     : super core::Object::•()
     ;
-  abstract method m(covariant core::num a) → void;
+  abstract method m(covariant core::num a) → core::Object?;
 }
 static method main() → dynamic {}
diff --git a/pkg/front_end/testcases/nnbd/infer_method_types.dart.weak.expect b/pkg/front_end/testcases/nnbd/infer_method_types.dart.weak.expect
index cc03fc1a27c..85e72a08854 100644
--- a/pkg/front_end/testcases/nnbd/infer_method_types.dart.weak.expect
+++ b/pkg/front_end/testcases/nnbd/infer_method_types.dart.weak.expect
@@ -48,7 +48,7 @@ abstract class H extends core::Object implements self::D, self::E, self::F, self
   synthetic constructor •() → self::H
     : super core::Object::•()
     ;
-  abstract forwarding-stub member-signature method m(covariant core::num a) → void;
+  abstract forwarding-stub member-signature method m(covariant core::num a) → core::Object?;
 }
 abstract class I extends core::Object implements self::D {
   synthetic constructor •() → self::I
@@ -60,18 +60,18 @@ abstract class J extends core::Object implements self::H {
   synthetic constructor •() → self::J
     : super core::Object::•()
     ;
-  abstract method m(covariant core::num a) → void;
+  abstract method m(covariant core::num a) → core::Object?;
 }
 abstract class K extends core::Object implements self::I, self::E, self::G {
   synthetic constructor •() → self::K
     : super core::Object::•()
     ;
-  abstract forwarding-stub member-signature method m(covariant core::num a) → void;
+  abstract forwarding-stub member-signature method m(covariant core::num a) → core::Object?;
 }
 abstract class L extends core::Object implements self::K {
   synthetic constructor •() → self::L
     : super core::Object::•()
     ;
-  abstract method m(covariant core::num a) → void;
+  abstract method m(covariant core::num a) → core::Object?;
 }
 static method main() → dynamic {}
diff --git a/pkg/front_end/testcases/nnbd/infer_method_types.dart.weak.transformed.expect b/pkg/front_end/testcases/nnbd/infer_method_types.dart.weak.transformed.expect
index cc03fc1a27c..85e72a08854 100644
--- a/pkg/front_end/testcases/nnbd/infer_method_types.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/infer_method_types.dart.weak.transformed.expect
@@ -48,7 +48,7 @@ abstract class H extends core::Object implements self::D, self::E, self::F, self
   synthetic constructor •() → self::H
     : super core::Object::•()
     ;
-  abstract forwarding-stub member-signature method m(covariant core::num a) → void;
+  abstract forwarding-stub member-signature method m(covariant core::num a) → core::Object?;
 }
 abstract class I extends core::Object implements self::D {
   synthetic constructor •() → self::I
@@ -60,18 +60,18 @@ abstract class J extends core::Object implements self::H {
   synthetic constructor •() → self::J
     : super core::Object::•()
     ;
-  abstract method m(covariant core::num a) → void;
+  abstract method m(covariant core::num a) → core::Object?;
 }
 abstract class K extends core::Object implements self::I, self::E, self::G {
   synthetic constructor •() → self::K
     : super core::Object::•()
     ;
-  abstract forwarding-stub member-signature method m(covariant core::num a) → void;
+  abstract forwarding-stub member-signature method m(covariant core::num a) → core::Object?;
 }
 abstract class L extends core::Object implements self::K {
   synthetic constructor •() → self::L
     : super core::Object::•()
     ;
-  abstract method m(covariant core::num a) → void;
+  abstract method m(covariant core::num a) → core::Object?;
 }
 static method main() → dynamic {}
diff --git a/pkg/front_end/testcases/nnbd/issue41567.dart b/pkg/front_end/testcases/nnbd/issue41567.dart
new file mode 100644
index 00000000000..9df55901081
--- /dev/null
+++ b/pkg/front_end/testcases/nnbd/issue41567.dart
@@ -0,0 +1,17 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'issue41567_lib.dart';
+
+class B extends A {}
+
+class in1 extends out_Object implements B {} // ok
+
+class in2 extends B implements out_Object {} // ok
+
+class in3 extends out_int implements B {} // error
+
+class in4 extends B implements out_int {} // error
+
+main() {}
diff --git a/pkg/front_end/testcases/nnbd/issue41567.dart.outline.expect b/pkg/front_end/testcases/nnbd/issue41567.dart.outline.expect
new file mode 100644
index 00000000000..4214a62dda3
--- /dev/null
+++ b/pkg/front_end/testcases/nnbd/issue41567.dart.outline.expect
@@ -0,0 +1,58 @@
+//
+// Problems in component:
+//
+// pkg/front_end/testcases/nnbd/issue41567.dart:13:7: Error: 'in3' can't implement both 'A<int>' and 'A<dynamic>'
+//  - 'A' is from 'pkg/front_end/testcases/nnbd/issue41567_lib.dart'.
+// class in3 extends out_int implements B {} // error
+//       ^
+//
+// pkg/front_end/testcases/nnbd/issue41567.dart:15:7: Error: 'in4' can't implement both 'A<dynamic>' and 'A<int>'
+//  - 'A' is from 'pkg/front_end/testcases/nnbd/issue41567_lib.dart'.
+// class in4 extends B implements out_int {} // error
+//       ^
+//
+library /*isNonNullableByDefault*/;
+import self as self;
+import "issue41567_lib.dart" as iss;
+
+import "org-dartlang-testcase:///issue41567_lib.dart";
+
+class B extends iss::A<dynamic> {
+  synthetic constructor •() → self::B
+    ;
+}
+class in1 extends iss::out_Object implements self::B {
+  synthetic constructor •() → self::in1
+    ;
+}
+class in2 extends self::B implements iss::out_Object {
+  synthetic constructor •() → self::in2
+    ;
+}
+class in3 extends iss::out_int implements self::B {
+  synthetic constructor •() → self::in3
+    ;
+}
+class in4 extends self::B implements iss::out_int {
+  synthetic constructor •() → self::in4
+    ;
+}
+static method main() → dynamic
+  ;
+
+library;
+import self as iss;
+import "dart:core" as core;
+
+class A<T extends core::Object* = dynamic> extends core::Object {
+  synthetic constructor •() → iss::A<iss::A::T*>*
+    ;
+}
+class out_int extends iss::A<core::int*> {
+  synthetic constructor •() → iss::out_int*
+    ;
+}
+class out_Object extends iss::A<core::Object*> {
+  synthetic constructor •() → iss::out_Object*
+    ;
+}
diff --git a/pkg/front_end/testcases/nnbd/issue41567.dart.strong.expect b/pkg/front_end/testcases/nnbd/issue41567.dart.strong.expect
new file mode 100644
index 00000000000..5ae9d2565d4
--- /dev/null
+++ b/pkg/front_end/testcases/nnbd/issue41567.dart.strong.expect
@@ -0,0 +1,65 @@
+//
+// Problems in component:
+//
+// pkg/front_end/testcases/nnbd/issue41567.dart:13:7: Error: 'in3' can't implement both 'A<int>' and 'A<dynamic>'
+//  - 'A' is from 'pkg/front_end/testcases/nnbd/issue41567_lib.dart'.
+// class in3 extends out_int implements B {} // error
+//       ^
+//
+// pkg/front_end/testcases/nnbd/issue41567.dart:15:7: Error: 'in4' can't implement both 'A<dynamic>' and 'A<int>'
+//  - 'A' is from 'pkg/front_end/testcases/nnbd/issue41567_lib.dart'.
+// class in4 extends B implements out_int {} // error
+//       ^
+//
+library /*isNonNullableByDefault*/;
+import self as self;
+import "issue41567_lib.dart" as iss;
+
+import "org-dartlang-testcase:///issue41567_lib.dart";
+
+class B extends iss::A<dynamic> {
+  synthetic constructor •() → self::B
+    : super iss::A::•()
+    ;
+}
+class in1 extends iss::out_Object implements self::B {
+  synthetic constructor •() → self::in1
+    : super iss::out_Object::•()
+    ;
+}
+class in2 extends self::B implements iss::out_Object {
+  synthetic constructor •() → self::in2
+    : super self::B::•()
+    ;
+}
+class in3 extends iss::out_int implements self::B {
+  synthetic constructor •() → self::in3
+    : super iss::out_int::•()
+    ;
+}
+class in4 extends self::B implements iss::out_int {
+  synthetic constructor •() → self::in4
+    : super self::B::•()
+    ;
+}
+static method main() → dynamic {}
+
+library;
+import self as iss;
+import "dart:core" as core;
+
+class A<T extends core::Object* = dynamic> extends core::Object {
+  synthetic constructor •() → iss::A<iss::A::T*>*
+    : super core::Object::•()
+    ;
+}
+class out_int extends iss::A<core::int*> {
+  synthetic constructor •() → iss::out_int*
+    : super iss::A::•()
+    ;
+}
+class out_Object extends iss::A<core::Object*> {
+  synthetic constructor •() → iss::out_Object*
+    : super iss::A::•()
+    ;
+}
diff --git a/pkg/front_end/testcases/nnbd/issue41567.dart.weak.expect b/pkg/front_end/testcases/nnbd/issue41567.dart.weak.expect
new file mode 100644
index 00000000000..5ae9d2565d4
--- /dev/null
+++ b/pkg/front_end/testcases/nnbd/issue41567.dart.weak.expect
@@ -0,0 +1,65 @@
+//
+// Problems in component:
+//
+// pkg/front_end/testcases/nnbd/issue41567.dart:13:7: Error: 'in3' can't implement both 'A<int>' and 'A<dynamic>'
+//  - 'A' is from 'pkg/front_end/testcases/nnbd/issue41567_lib.dart'.
+// class in3 extends out_int implements B {} // error
+//       ^
+//
+// pkg/front_end/testcases/nnbd/issue41567.dart:15:7: Error: 'in4' can't implement both 'A<dynamic>' and 'A<int>'
+//  - 'A' is from 'pkg/front_end/testcases/nnbd/issue41567_lib.dart'.
+// class in4 extends B implements out_int {} // error
+//       ^
+//
+library /*isNonNullableByDefault*/;
+import self as self;
+import "issue41567_lib.dart" as iss;
+
+import "org-dartlang-testcase:///issue41567_lib.dart";
+
+class B extends iss::A<dynamic> {
+  synthetic constructor •() → self::B
+    : super iss::A::•()
+    ;
+}
+class in1 extends iss::out_Object implements self::B {
+  synthetic constructor •() → self::in1
+    : super iss::out_Object::•()
+    ;
+}
+class in2 extends self::B implements iss::out_Object {
+  synthetic constructor •() → self::in2
+    : super self::B::•()
+    ;
+}
+class in3 extends iss::out_int implements self::B {
+  synthetic constructor •() → self::in3
+    : super iss::out_int::•()
+    ;
+}
+class in4 extends self::B implements iss::out_int {
+  synthetic constructor •() → self::in4
+    : super self::B::•()
+    ;
+}
+static method main() → dynamic {}
+
+library;
+import self as iss;
+import "dart:core" as core;
+
+class A<T extends core::Object* = dynamic> extends core::Object {
+  synthetic constructor •() → iss::A<iss::A::T*>*
+    : super core::Object::•()
+    ;
+}
+class out_int extends iss::A<core::int*> {
+  synthetic constructor •() → iss::out_int*
+    : super iss::A::•()
+    ;
+}
+class out_Object extends iss::A<core::Object*> {
+  synthetic constructor •() → iss::out_Object*
+    : super iss::A::•()
+    ;
+}
diff --git a/pkg/front_end/testcases/nnbd/issue41567_lib.dart b/pkg/front_end/testcases/nnbd/issue41567_lib.dart
new file mode 100644
index 00000000000..e45bcd9a40c
--- /dev/null
+++ b/pkg/front_end/testcases/nnbd/issue41567_lib.dart
@@ -0,0 +1,11 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// @dart=2.6
+
+class A<T> {}
+
+class out_int extends A<int> {}
+
+class out_Object extends A<Object> {}
diff --git a/pkg/front_end/testcases/outline.status b/pkg/front_end/testcases/outline.status
index ca35b47ab32..8103acb98f3 100644
--- a/pkg/front_end/testcases/outline.status
+++ b/pkg/front_end/testcases/outline.status
@@ -40,6 +40,7 @@ inference/mixin_inference_outwards_4: TypeCheckError
 inference/mixin_inference_unification_1: TypeCheckError
 inference/mixin_inference_unification_2: TypeCheckError
 nnbd/inheritance_from_opt_in: TypeCheckError
+nnbd/issue41567: TypeCheckError
 nnbd/messages_with_types_opt_in: TypeCheckError
 nnbd/messages_with_types_opt_out: TypeCheckError
 nnbd/never_opt_out: TypeCheckError
diff --git a/pkg/front_end/testcases/strong.status b/pkg/front_end/testcases/strong.status
index fb0f63b534c..907af6e9143 100644
--- a/pkg/front_end/testcases/strong.status
+++ b/pkg/front_end/testcases/strong.status
@@ -167,6 +167,7 @@ instantiate_to_bound/non_simple_class_parametrized_typedef_cycle: RuntimeError #
 instantiate_to_bound/non_simple_generic_function_in_bound_regress: RuntimeError # Expected
 nnbd/inheritance_from_opt_in: TypeCheckError
 nnbd/issue41180: RuntimeError # Strong mode runtime checking fails due to mixed strong mode.
+nnbd/issue41567: TypeCheckError
 nnbd/messages_with_types_opt_in: TypeCheckError
 nnbd/messages_with_types_opt_out: TypeCheckError
 nnbd/never_opt_out: TypeCheckError
diff --git a/pkg/front_end/testcases/text_serialization.status b/pkg/front_end/testcases/text_serialization.status
index d42f2cb7143..41d9cf99cc5 100644
--- a/pkg/front_end/testcases/text_serialization.status
+++ b/pkg/front_end/testcases/text_serialization.status
@@ -165,6 +165,7 @@ instantiate_to_bound/non_simple_class_parametrized_typedef_cycle: RuntimeError
 instantiate_to_bound/non_simple_generic_function_in_bound_regress: RuntimeError
 nnbd/inheritance_from_opt_in: TypeCheckError
 nnbd/issue41180: RuntimeError
+nnbd/issue41567: TypeCheckError
 nnbd/messages_with_types_opt_in: TypeCheckError
 nnbd/messages_with_types_opt_out: TypeCheckError
 nnbd/never_opt_out: TypeCheckError
diff --git a/pkg/front_end/testcases/weak.status b/pkg/front_end/testcases/weak.status
index 23e902357bb..4de00b084ea 100644
--- a/pkg/front_end/testcases/weak.status
+++ b/pkg/front_end/testcases/weak.status
@@ -59,6 +59,7 @@ general_nnbd_opt_out/type_variable_bound_access: TypeCheckError
 general_nnbd_opt_out/unsound_promotion: TypeCheckError
 general_nnbd_opt_out/void_methods: RuntimeError
 nnbd/inheritance_from_opt_in: TypeCheckError
+nnbd/issue41567: TypeCheckError
 nnbd/messages_with_types_opt_in: TypeCheckError
 nnbd/messages_with_types_opt_out: TypeCheckError
 nnbd/never_opt_out: TypeCheckError
diff --git a/pkg/kernel/lib/src/nnbd_top_merge.dart b/pkg/kernel/lib/src/nnbd_top_merge.dart
index 317b1df612e..f0c5b4e71c5 100644
--- a/pkg/kernel/lib/src/nnbd_top_merge.dart
+++ b/pkg/kernel/lib/src/nnbd_top_merge.dart
@@ -55,8 +55,8 @@ class NnbdTopMergeVisitor extends MergeVisitor {
         // NNBD_TOP_MERGE(Object?, dynamic) = Object?
         return coreTypes.objectNullableRawType;
       } else if (b is VoidType) {
-        // NNBD_TOP_MERGE(Object?, void) = void
-        return const VoidType();
+        // NNBD_TOP_MERGE(Object?, void) = Object?
+        return coreTypes.objectNullableRawType;
       } else if (b == coreTypes.objectNullableRawType) {
         // NNBD_TOP_MERGE(Object?, Object?) = Object?
         return coreTypes.objectNullableRawType;
@@ -66,8 +66,8 @@ class NnbdTopMergeVisitor extends MergeVisitor {
         // NNBD_TOP_MERGE(Object*, dynamic) = Object?
         return coreTypes.objectNullableRawType;
       } else if (b is VoidType) {
-        // NNBD_TOP_MERGE(Object*, void) = void
-        return const VoidType();
+        // NNBD_TOP_MERGE(Object*, void) = Object?
+        return coreTypes.objectNullableRawType;
       }
     } else if (a == coreTypes.nullType &&
         b is NeverType &&
@@ -81,17 +81,17 @@ class NnbdTopMergeVisitor extends MergeVisitor {
   @override
   DartType visitVoidType(VoidType a, DartType b) {
     if (b is DynamicType) {
-      // NNBD_TOP_MERGE(void, dynamic) = void
-      return const VoidType();
+      // NNBD_TOP_MERGE(void, dynamic) = Object?
+      return coreTypes.objectNullableRawType;
     } else if (b is VoidType) {
       // NNBD_TOP_MERGE(void, void) = void
       return const VoidType();
     } else if (b == coreTypes.objectNullableRawType) {
-      // NNBD_TOP_MERGE(void, Object?) = void
-      return const VoidType();
+      // NNBD_TOP_MERGE(void, Object?) = Object?
+      return coreTypes.objectNullableRawType;
     } else if (b == coreTypes.objectLegacyRawType) {
-      // NNBD_TOP_MERGE(void, Object*) = void
-      return const VoidType();
+      // NNBD_TOP_MERGE(void, Object*) = Object?
+      return coreTypes.objectNullableRawType;
     }
     return null;
   }
@@ -102,8 +102,8 @@ class NnbdTopMergeVisitor extends MergeVisitor {
       // NNBD_TOP_MERGE(dynamic, dynamic) = dynamic
       return const DynamicType();
     } else if (b is VoidType) {
-      // NNBD_TOP_MERGE(dynamic, void) = void
-      return const VoidType();
+      // NNBD_TOP_MERGE(dynamic, void) = Object?
+      return coreTypes.objectNullableRawType;
     } else if (b == coreTypes.objectNullableRawType) {
       // NNBD_TOP_MERGE(dynamic, Object?) = Object?
       return coreTypes.objectNullableRawType;
diff --git a/pkg/kernel/test/nnbd_top_merge_test.dart b/pkg/kernel/test/nnbd_top_merge_test.dart
index da9bd8d89dd..4eb5d4069da 100644
--- a/pkg/kernel/test/nnbd_top_merge_test.dart
+++ b/pkg/kernel/test/nnbd_top_merge_test.dart
@@ -17,10 +17,10 @@ const Map<String, dynamic> data = {
   'Object vs Object': 'Object',
   'dynamic vs dynamic': 'dynamic',
   'void vs void': 'void',
-  'Object? vs void': 'void',
-  'Object* vs void': 'void',
+  'Object? vs void': 'Object?',
+  'Object* vs void': 'Object?',
   'Object vs void': null,
-  'dynamic vs void': 'void',
+  'dynamic vs void': 'Object?',
   'Object? vs dynamic': 'Object?',
   'Object* vs dynamic': 'Object?',
   'Object vs dynamic': null,
@@ -41,10 +41,10 @@ const Map<String, dynamic> data = {
   'List<Object> vs List<Object>': 'List<Object>',
   'List<dynamic> vs List<dynamic>': 'List<dynamic>',
   'List<void> vs List<void>': 'List<void>',
-  'List<Object?> vs List<void>': 'List<void>',
-  'List<Object*> vs List<void>': 'List<void>',
+  'List<Object?> vs List<void>': 'List<Object?>',
+  'List<Object*> vs List<void>': 'List<Object?>',
   'List<Object> vs List<void>': null,
-  'List<dynamic> vs List<void>': 'List<void>',
+  'List<dynamic> vs List<void>': 'List<Object?>',
   'List<Object?> vs List<dynamic>': 'List<Object?>',
   'List<Object*> vs List<dynamic>': 'List<Object?>',
   'List<Object> vs List<dynamic>': null,