diff --git a/DEPS b/DEPS
index c646483fdcf..ffeacc6b6b9 100644
--- a/DEPS
+++ b/DEPS
@@ -469,7 +469,7 @@ deps = {
     "packages": [
       {
         "package": "dart/cfe/dart2js_dills",
-        "version": "binary_version:41_2",
+        "version": "binary_version:42",
       }
     ],
     "dep_type": "cipd",
diff --git a/pkg/front_end/lib/src/fasta/builder/field_builder.dart b/pkg/front_end/lib/src/fasta/builder/field_builder.dart
index 9e1d7c20dbe..5cb9fc05b9c 100644
--- a/pkg/front_end/lib/src/fasta/builder/field_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/field_builder.dart
@@ -674,12 +674,14 @@ abstract class AbstractLateFieldEncoding implements FieldEncoding {
         new Field(null, fileUri: fileUri, reference: referenceFrom?.reference)
           ..fileOffset = charOffset
           ..fileEndOffset = charEndOffset
-          ..isNonNullableByDefault = true;
+          ..isNonNullableByDefault = true
+          ..isInternalImplementation = true;
     _lateIsSetField = new Field(null,
         fileUri: fileUri, reference: lateIsSetReferenceFrom?.reference)
       ..fileOffset = charOffset
       ..fileEndOffset = charEndOffset
-      ..isNonNullableByDefault = true;
+      ..isNonNullableByDefault = true
+      ..isInternalImplementation = true;
     _lateGetter = new Procedure(
         null, ProcedureKind.Getter, new FunctionNode(null),
         fileUri: fileUri, reference: getterReferenceFrom?.reference)
diff --git a/pkg/front_end/lib/src/fasta/dill/dill_member_builder.dart b/pkg/front_end/lib/src/fasta/dill/dill_member_builder.dart
index 40f72852ae9..93becfc7252 100644
--- a/pkg/front_end/lib/src/fasta/dill/dill_member_builder.dart
+++ b/pkg/front_end/lib/src/fasta/dill/dill_member_builder.dart
@@ -155,11 +155,11 @@ class DillClassMember extends BuilderClassMember {
   @override
   bool get isSourceDeclaration => false;
 
-  // TODO(johnniwinther): This should be `true` for fields added for late
-  // lowering. Currently not needed because these fields are private and we only
-  // use this property while checking implementation of abstract members.
   @override
-  bool get isInternalImplementation => false;
+  bool get isInternalImplementation {
+    Member member = memberBuilder.member;
+    return member is Field && member.isInternalImplementation;
+  }
 
   @override
   bool get isProperty =>
diff --git a/pkg/front_end/test/spell_checking_list_tests.txt b/pkg/front_end/test/spell_checking_list_tests.txt
index 7add1d4be82..44f1f7775b5 100644
--- a/pkg/front_end/test/spell_checking_list_tests.txt
+++ b/pkg/front_end/test/spell_checking_list_tests.txt
@@ -275,6 +275,7 @@ ioo
 isolate
 isolates
 issue41210b
+issue41436c
 iter
 joo
 jumped
diff --git a/pkg/front_end/testcases/late_lowering/issue41436c/issue41436c.dart b/pkg/front_end/testcases/late_lowering/issue41436c/issue41436c.dart
new file mode 100644
index 00000000000..ec85c08b7d6
--- /dev/null
+++ b/pkg/front_end/testcases/late_lowering/issue41436c/issue41436c.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.
+
+import 'issue41436c_lib.dart';
+
+class C extends B {}
+
+main() {
+  new C();
+}
diff --git a/pkg/front_end/testcases/late_lowering/issue41436c/issue41436c_lib.dart b/pkg/front_end/testcases/late_lowering/issue41436c/issue41436c_lib.dart
new file mode 100644
index 00000000000..d7adb144358
--- /dev/null
+++ b/pkg/front_end/testcases/late_lowering/issue41436c/issue41436c_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.
+
+abstract class A {
+  late int x;
+}
+
+class B implements A {
+  int x = 3;
+}
diff --git a/pkg/front_end/testcases/late_lowering/issue41436c/issue41436c_lib.dart.outline.expect b/pkg/front_end/testcases/late_lowering/issue41436c/issue41436c_lib.dart.outline.expect
new file mode 100644
index 00000000000..de879f18d45
--- /dev/null
+++ b/pkg/front_end/testcases/late_lowering/issue41436c/issue41436c_lib.dart.outline.expect
@@ -0,0 +1,34 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "issue41436c_lib.dart" as iss;
+import "dart:core" as core;
+
+import "org-dartlang-testcase:///issue41436c_lib.dart";
+
+class C extends iss::B {
+  synthetic constructor •() → self::C
+    ;
+  no-such-method-forwarder get /* from org-dartlang-testcase:///issue41436c_lib.dart */ _#A#x() → core::int?
+    return this.{core::Object::noSuchMethod}(new core::_InvocationMirror::_withType(#_#A#x, 1, const <core::Type*>[], const <dynamic>[], core::Map::unmodifiable<core::Symbol*, dynamic>(const <core::Symbol*, dynamic>{}))) as{TypeError,ForDynamic,ForNonNullableByDefault} core::int?;
+  no-such-method-forwarder set /* from org-dartlang-testcase:///issue41436c_lib.dart */ _#A#x(core::int? value) → void
+    return this.{core::Object::noSuchMethod}(new core::_InvocationMirror::_withType(#_#A#x=, 2, const <core::Type*>[], core::List::unmodifiable<dynamic>(<dynamic>[value]), core::Map::unmodifiable<core::Symbol*, dynamic>(const <core::Symbol*, dynamic>{})));
+}
+static method main() → dynamic
+  ;
+
+library /*isNonNullableByDefault*/;
+import self as iss;
+import "dart:core" as core;
+
+abstract class A extends core::Object {
+  field core::int? _#A#x;
+  synthetic constructor •() → iss::A
+    ;
+  get x() → core::int;
+  set x(core::int #t1) → void;
+}
+class B extends core::Object implements iss::A {
+  field core::int x;
+  synthetic constructor •() → iss::B
+    ;
+}
diff --git a/pkg/front_end/testcases/late_lowering/issue41436c/issue41436c_lib.dart.strong.expect b/pkg/front_end/testcases/late_lowering/issue41436c/issue41436c_lib.dart.strong.expect
new file mode 100644
index 00000000000..05bf5e38b58
--- /dev/null
+++ b/pkg/front_end/testcases/late_lowering/issue41436c/issue41436c_lib.dart.strong.expect
@@ -0,0 +1,49 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "issue41436c_lib.dart" as iss;
+import "dart:core" as core;
+
+import "org-dartlang-testcase:///issue41436c_lib.dart";
+
+class C extends iss::B {
+  synthetic constructor •() → self::C
+    : super iss::B::•()
+    ;
+  no-such-method-forwarder get /* from org-dartlang-testcase:///issue41436c_lib.dart */ _#A#x() → core::int?
+    return this.{core::Object::noSuchMethod}(new core::_InvocationMirror::_withType(#C1, 1, #C2, #C3, core::Map::unmodifiable<core::Symbol*, dynamic>(#C4))) as{TypeError,ForDynamic,ForNonNullableByDefault} core::int?;
+  no-such-method-forwarder set /* from org-dartlang-testcase:///issue41436c_lib.dart */ _#A#x(core::int? value) → void
+    return this.{core::Object::noSuchMethod}(new core::_InvocationMirror::_withType(#C5, 2, #C2, core::List::unmodifiable<dynamic>(<dynamic>[value]), core::Map::unmodifiable<core::Symbol*, dynamic>(#C4)));
+}
+static method main() → dynamic {
+  new self::C::•();
+}
+
+library /*isNonNullableByDefault*/;
+import self as iss;
+import "dart:core" as core;
+import "dart:_internal" as _in;
+
+abstract class A extends core::Object {
+  field core::int? _#A#x = null;
+  synthetic constructor •() → iss::A
+    : super core::Object::•()
+    ;
+  get x() → core::int
+    return let final core::int? #t1 = this.{iss::A::_#A#x} in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.") : #t1{core::int};
+  set x(core::int #t2) → void
+    this.{iss::A::_#A#x} = #t2;
+}
+class B extends core::Object implements iss::A {
+  field core::int x = 3;
+  synthetic constructor •() → iss::B
+    : super core::Object::•()
+    ;
+}
+
+constants  {
+  #C1 = #org-dartlang-testcase:///issue41436c.dart::_#A#x
+  #C2 = <core::Type*>[]
+  #C3 = <dynamic>[]
+  #C4 = core::_ImmutableMap<core::Symbol*, dynamic> {_kvPairs:#C3}
+  #C5 = #org-dartlang-testcase:///issue41436c.dart::_#A#x=
+}
diff --git a/pkg/front_end/testcases/late_lowering/issue41436c/issue41436c_lib.dart.strong.transformed.expect b/pkg/front_end/testcases/late_lowering/issue41436c/issue41436c_lib.dart.strong.transformed.expect
new file mode 100644
index 00000000000..05bf5e38b58
--- /dev/null
+++ b/pkg/front_end/testcases/late_lowering/issue41436c/issue41436c_lib.dart.strong.transformed.expect
@@ -0,0 +1,49 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "issue41436c_lib.dart" as iss;
+import "dart:core" as core;
+
+import "org-dartlang-testcase:///issue41436c_lib.dart";
+
+class C extends iss::B {
+  synthetic constructor •() → self::C
+    : super iss::B::•()
+    ;
+  no-such-method-forwarder get /* from org-dartlang-testcase:///issue41436c_lib.dart */ _#A#x() → core::int?
+    return this.{core::Object::noSuchMethod}(new core::_InvocationMirror::_withType(#C1, 1, #C2, #C3, core::Map::unmodifiable<core::Symbol*, dynamic>(#C4))) as{TypeError,ForDynamic,ForNonNullableByDefault} core::int?;
+  no-such-method-forwarder set /* from org-dartlang-testcase:///issue41436c_lib.dart */ _#A#x(core::int? value) → void
+    return this.{core::Object::noSuchMethod}(new core::_InvocationMirror::_withType(#C5, 2, #C2, core::List::unmodifiable<dynamic>(<dynamic>[value]), core::Map::unmodifiable<core::Symbol*, dynamic>(#C4)));
+}
+static method main() → dynamic {
+  new self::C::•();
+}
+
+library /*isNonNullableByDefault*/;
+import self as iss;
+import "dart:core" as core;
+import "dart:_internal" as _in;
+
+abstract class A extends core::Object {
+  field core::int? _#A#x = null;
+  synthetic constructor •() → iss::A
+    : super core::Object::•()
+    ;
+  get x() → core::int
+    return let final core::int? #t1 = this.{iss::A::_#A#x} in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.") : #t1{core::int};
+  set x(core::int #t2) → void
+    this.{iss::A::_#A#x} = #t2;
+}
+class B extends core::Object implements iss::A {
+  field core::int x = 3;
+  synthetic constructor •() → iss::B
+    : super core::Object::•()
+    ;
+}
+
+constants  {
+  #C1 = #org-dartlang-testcase:///issue41436c.dart::_#A#x
+  #C2 = <core::Type*>[]
+  #C3 = <dynamic>[]
+  #C4 = core::_ImmutableMap<core::Symbol*, dynamic> {_kvPairs:#C3}
+  #C5 = #org-dartlang-testcase:///issue41436c.dart::_#A#x=
+}
diff --git a/pkg/front_end/testcases/late_lowering/issue41436c/issue41436c_lib.dart.weak.expect b/pkg/front_end/testcases/late_lowering/issue41436c/issue41436c_lib.dart.weak.expect
new file mode 100644
index 00000000000..05bf5e38b58
--- /dev/null
+++ b/pkg/front_end/testcases/late_lowering/issue41436c/issue41436c_lib.dart.weak.expect
@@ -0,0 +1,49 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "issue41436c_lib.dart" as iss;
+import "dart:core" as core;
+
+import "org-dartlang-testcase:///issue41436c_lib.dart";
+
+class C extends iss::B {
+  synthetic constructor •() → self::C
+    : super iss::B::•()
+    ;
+  no-such-method-forwarder get /* from org-dartlang-testcase:///issue41436c_lib.dart */ _#A#x() → core::int?
+    return this.{core::Object::noSuchMethod}(new core::_InvocationMirror::_withType(#C1, 1, #C2, #C3, core::Map::unmodifiable<core::Symbol*, dynamic>(#C4))) as{TypeError,ForDynamic,ForNonNullableByDefault} core::int?;
+  no-such-method-forwarder set /* from org-dartlang-testcase:///issue41436c_lib.dart */ _#A#x(core::int? value) → void
+    return this.{core::Object::noSuchMethod}(new core::_InvocationMirror::_withType(#C5, 2, #C2, core::List::unmodifiable<dynamic>(<dynamic>[value]), core::Map::unmodifiable<core::Symbol*, dynamic>(#C4)));
+}
+static method main() → dynamic {
+  new self::C::•();
+}
+
+library /*isNonNullableByDefault*/;
+import self as iss;
+import "dart:core" as core;
+import "dart:_internal" as _in;
+
+abstract class A extends core::Object {
+  field core::int? _#A#x = null;
+  synthetic constructor •() → iss::A
+    : super core::Object::•()
+    ;
+  get x() → core::int
+    return let final core::int? #t1 = this.{iss::A::_#A#x} in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.") : #t1{core::int};
+  set x(core::int #t2) → void
+    this.{iss::A::_#A#x} = #t2;
+}
+class B extends core::Object implements iss::A {
+  field core::int x = 3;
+  synthetic constructor •() → iss::B
+    : super core::Object::•()
+    ;
+}
+
+constants  {
+  #C1 = #org-dartlang-testcase:///issue41436c.dart::_#A#x
+  #C2 = <core::Type*>[]
+  #C3 = <dynamic>[]
+  #C4 = core::_ImmutableMap<core::Symbol*, dynamic> {_kvPairs:#C3}
+  #C5 = #org-dartlang-testcase:///issue41436c.dart::_#A#x=
+}
diff --git a/pkg/front_end/testcases/late_lowering/issue41436c/issue41436c_lib.dart.weak.transformed.expect b/pkg/front_end/testcases/late_lowering/issue41436c/issue41436c_lib.dart.weak.transformed.expect
new file mode 100644
index 00000000000..05bf5e38b58
--- /dev/null
+++ b/pkg/front_end/testcases/late_lowering/issue41436c/issue41436c_lib.dart.weak.transformed.expect
@@ -0,0 +1,49 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "issue41436c_lib.dart" as iss;
+import "dart:core" as core;
+
+import "org-dartlang-testcase:///issue41436c_lib.dart";
+
+class C extends iss::B {
+  synthetic constructor •() → self::C
+    : super iss::B::•()
+    ;
+  no-such-method-forwarder get /* from org-dartlang-testcase:///issue41436c_lib.dart */ _#A#x() → core::int?
+    return this.{core::Object::noSuchMethod}(new core::_InvocationMirror::_withType(#C1, 1, #C2, #C3, core::Map::unmodifiable<core::Symbol*, dynamic>(#C4))) as{TypeError,ForDynamic,ForNonNullableByDefault} core::int?;
+  no-such-method-forwarder set /* from org-dartlang-testcase:///issue41436c_lib.dart */ _#A#x(core::int? value) → void
+    return this.{core::Object::noSuchMethod}(new core::_InvocationMirror::_withType(#C5, 2, #C2, core::List::unmodifiable<dynamic>(<dynamic>[value]), core::Map::unmodifiable<core::Symbol*, dynamic>(#C4)));
+}
+static method main() → dynamic {
+  new self::C::•();
+}
+
+library /*isNonNullableByDefault*/;
+import self as iss;
+import "dart:core" as core;
+import "dart:_internal" as _in;
+
+abstract class A extends core::Object {
+  field core::int? _#A#x = null;
+  synthetic constructor •() → iss::A
+    : super core::Object::•()
+    ;
+  get x() → core::int
+    return let final core::int? #t1 = this.{iss::A::_#A#x} in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.") : #t1{core::int};
+  set x(core::int #t2) → void
+    this.{iss::A::_#A#x} = #t2;
+}
+class B extends core::Object implements iss::A {
+  field core::int x = 3;
+  synthetic constructor •() → iss::B
+    : super core::Object::•()
+    ;
+}
+
+constants  {
+  #C1 = #org-dartlang-testcase:///issue41436c.dart::_#A#x
+  #C2 = <core::Type*>[]
+  #C3 = <dynamic>[]
+  #C4 = core::_ImmutableMap<core::Symbol*, dynamic> {_kvPairs:#C3}
+  #C5 = #org-dartlang-testcase:///issue41436c.dart::_#A#x=
+}
diff --git a/pkg/front_end/testcases/late_lowering/issue41436c/link.options b/pkg/front_end/testcases/late_lowering/issue41436c/link.options
new file mode 100644
index 00000000000..8503704a0f4
--- /dev/null
+++ b/pkg/front_end/testcases/late_lowering/issue41436c/link.options
@@ -0,0 +1 @@
+issue41436c_lib.dart
\ No newline at end of file
diff --git a/pkg/front_end/testcases/text_serialization.status b/pkg/front_end/testcases/text_serialization.status
index 745dd0fa0fb..467c8fabb69 100644
--- a/pkg/front_end/testcases/text_serialization.status
+++ b/pkg/front_end/testcases/text_serialization.status
@@ -1264,6 +1264,7 @@ late_lowering/issue40601: TextSerializationFailure
 late_lowering/issue40805: TextSerializationFailure
 late_lowering/issue41436/issue41436: TextSerializationFailure
 late_lowering/issue41436b: TextSerializationFailure
+late_lowering/issue41436c/issue41436c: TextSerializationFailure
 late_lowering/late_field_inference: TextSerializationFailure
 late_lowering/late_field_with_initializer: TextSerializationFailure
 late_lowering/late_field_without_initializer: TextSerializationFailure
diff --git a/pkg/kernel/binary.md b/pkg/kernel/binary.md
index 5f9a2389746..3c70beba08f 100644
--- a/pkg/kernel/binary.md
+++ b/pkg/kernel/binary.md
@@ -143,7 +143,7 @@ type CanonicalName {
 
 type ComponentFile {
   UInt32 magic = 0x90ABCDEF;
-  UInt32 formatVersion = 41;
+  UInt32 formatVersion = 42;
   List<String> problemsAsJson; // Described in problems.md.
   Library[] libraries;
   UriSource sourceMap;
@@ -371,7 +371,7 @@ type Field extends Member {
   FileOffset fileEndOffset;
   UInt flags (isFinal, isConst, isStatic, hasImplicitGetter, hasImplicitSetter,
                 isCovariant, isGenericCovariantImpl, isLate, isExtensionMember,
-                isNonNullableByDefault);
+                isNonNullableByDefault, isInternalImplementation);
   Name name;
   List<Expression> annotations;
   DartType type;
diff --git a/pkg/kernel/lib/ast.dart b/pkg/kernel/lib/ast.dart
index 0a26190a978..e51b0a846e3 100644
--- a/pkg/kernel/lib/ast.dart
+++ b/pkg/kernel/lib/ast.dart
@@ -1739,6 +1739,7 @@ class Field extends Member {
   static const int FlagLate = 1 << 7;
   static const int FlagExtensionMember = 1 << 8;
   static const int FlagNonNullableByDefault = 1 << 9;
+  static const int FlagInternalImplementation = 1 << 10;
 
   /// Whether the field is declared with the `covariant` keyword.
   bool get isCovariant => flags & FlagCovariant != 0;
@@ -1780,6 +1781,13 @@ class Field extends Member {
   /// Whether the field is declared with the `late` keyword.
   bool get isLate => flags & FlagLate != 0;
 
+  // If `true` this field is not part of the interface but only part of the
+  // class members.
+  //
+  // This is `true` for instance for synthesized fields added for the late
+  // lowering.
+  bool get isInternalImplementation => flags & FlagInternalImplementation != 0;
+
   void set isCovariant(bool value) {
     flags = value ? (flags | FlagCovariant) : (flags & ~FlagCovariant);
   }
@@ -1823,6 +1831,12 @@ class Field extends Member {
     flags = value ? (flags | FlagLate) : (flags & ~FlagLate);
   }
 
+  void set isInternalImplementation(bool value) {
+    flags = value
+        ? (flags | FlagInternalImplementation)
+        : (flags & ~FlagInternalImplementation);
+  }
+
   /// True if the field is neither final nor const.
   bool get isMutable => flags & (FlagFinal | FlagConst) == 0;
   bool get isInstanceMember => !isStatic;
diff --git a/pkg/kernel/lib/binary/tag.dart b/pkg/kernel/lib/binary/tag.dart
index 1157e570dff..cec230824aa 100644
--- a/pkg/kernel/lib/binary/tag.dart
+++ b/pkg/kernel/lib/binary/tag.dart
@@ -149,7 +149,7 @@ class Tag {
   /// Internal version of kernel binary format.
   /// Bump it when making incompatible changes in kernel binaries.
   /// Keep in sync with runtime/vm/kernel_binary.h, pkg/kernel/binary.md.
-  static const int BinaryFormatVersion = 41;
+  static const int BinaryFormatVersion = 42;
 }
 
 abstract class ConstantTag {
diff --git a/runtime/vm/kernel_binary.h b/runtime/vm/kernel_binary.h
index aa906255343..4ceb1c78e72 100644
--- a/runtime/vm/kernel_binary.h
+++ b/runtime/vm/kernel_binary.h
@@ -20,7 +20,7 @@ static const uint32_t kMagicProgramFile = 0x90ABCDEFu;
 
 // Both version numbers are inclusive.
 static const uint32_t kMinSupportedKernelFormatVersion = 29;
-static const uint32_t kMaxSupportedKernelFormatVersion = 41;
+static const uint32_t kMaxSupportedKernelFormatVersion = 42;
 
 // Keep in sync with package:kernel/lib/binary/tag.dart
 #define KERNEL_TAG_LIST(V)                                                     \