diff --git a/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart b/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
index 6e433798ea6b..9d5ee44e9956 100644
--- a/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
+++ b/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
@@ -845,7 +845,8 @@ class TypeInferrerImpl implements TypeInferrer {
       }
       if (includeExtensionMethods) {
         ObjectAccessTarget target = _findExtensionMember(
-            receiverBound, coreTypes.objectClass, name, fileOffset);
+            receiverBound, coreTypes.objectClass, name, fileOffset,
+            setter: setter);
         if (target != null) {
           return target;
         }
diff --git a/pkg/front_end/testcases/nnbd/nullable_setter.dart b/pkg/front_end/testcases/nnbd/nullable_setter.dart
new file mode 100644
index 000000000000..8e9d230fab22
--- /dev/null
+++ b/pkg/front_end/testcases/nnbd/nullable_setter.dart
@@ -0,0 +1,32 @@
+// Copyright (c) 2019, 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.
+
+class C {
+  String m = "";
+  void set setter(String v) {}
+  void operator []=(int index, String value) {}
+}
+
+extension on C? {
+  void set setter(String v) {
+    this?.m = v;
+  }
+
+  void operator []=(int index, String value) {
+    this?.m = '$index$value';
+  }
+}
+
+main() {
+  C? c = new C();
+  expect("", c?.m);
+  c.setter = "42";
+  expect("42", c?.m);
+  c[42] = "87";
+  expect("4287", c?.m);
+}
+
+expect(expected, actual) {
+  if (expected != actual) throw 'Expected $expected, actual $actual';
+}
diff --git a/pkg/front_end/testcases/nnbd/nullable_setter.dart.outline.expect b/pkg/front_end/testcases/nnbd/nullable_setter.dart.outline.expect
new file mode 100644
index 000000000000..3f88610e5abb
--- /dev/null
+++ b/pkg/front_end/testcases/nnbd/nullable_setter.dart.outline.expect
@@ -0,0 +1,25 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:core" as core;
+
+class C extends core::Object {
+  field core::String m;
+  synthetic constructor •() → self::C
+    ;
+  set setter(core::String v) → void
+    ;
+  operator []=(core::int index, core::String value) → void
+    ;
+}
+extension _extension#0 on self::C? {
+  operator []= = self::_extension#0|[]=;
+  set setter = self::_extension#0|set#setter;
+}
+static method _extension#0|set#setter(final self::C? #this, core::String v) → void
+  ;
+static method _extension#0|[]=(final self::C? #this, core::int index, core::String value) → void
+  ;
+static method main() → dynamic
+  ;
+static method expect(dynamic expected, dynamic actual) → dynamic
+  ;
diff --git a/pkg/front_end/testcases/nnbd/nullable_setter.dart.strong.expect b/pkg/front_end/testcases/nnbd/nullable_setter.dart.strong.expect
new file mode 100644
index 000000000000..d36785469a17
--- /dev/null
+++ b/pkg/front_end/testcases/nnbd/nullable_setter.dart.strong.expect
@@ -0,0 +1,34 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:core" as core;
+
+class C extends core::Object {
+  field core::String m = "";
+  synthetic constructor •() → self::C
+    : super core::Object::•()
+    ;
+  set setter(core::String v) → void {}
+  operator []=(core::int index, core::String value) → void {}
+}
+extension _extension#0 on self::C? {
+  operator []= = self::_extension#0|[]=;
+  set setter = self::_extension#0|set#setter;
+}
+static method _extension#0|set#setter(final self::C? #this, core::String v) → void {
+  let final self::C? #t1 = #this in #t1.{core::Object::==}(null) ?{core::String?} null : #t1{self::C}.{self::C::m} = v;
+}
+static method _extension#0|[]=(final self::C? #this, core::int index, core::String value) → void {
+  let final self::C? #t2 = #this in #t2.{core::Object::==}(null) ?{core::String?} null : #t2{self::C}.{self::C::m} = "${index}${value}";
+}
+static method main() → dynamic {
+  self::C? c = new self::C::•();
+  self::expect("", let final self::C? #t3 = c in #t3.{core::Object::==}(null) ?{core::String?} null : #t3{self::C}.{self::C::m});
+  self::_extension#0|set#setter(c, "42");
+  self::expect("42", let final self::C? #t4 = c in #t4.{core::Object::==}(null) ?{core::String?} null : #t4{self::C}.{self::C::m});
+  self::_extension#0|[]=(c, 42, "87");
+  self::expect("4287", let final self::C? #t5 = c in #t5.{core::Object::==}(null) ?{core::String?} null : #t5{self::C}.{self::C::m});
+}
+static method expect(dynamic expected, dynamic actual) → dynamic {
+  if(!expected.{core::Object::==}(actual))
+    throw "Expected ${expected}, actual ${actual}";
+}
diff --git a/pkg/front_end/testcases/nnbd/nullable_setter.dart.strong.transformed.expect b/pkg/front_end/testcases/nnbd/nullable_setter.dart.strong.transformed.expect
new file mode 100644
index 000000000000..d36785469a17
--- /dev/null
+++ b/pkg/front_end/testcases/nnbd/nullable_setter.dart.strong.transformed.expect
@@ -0,0 +1,34 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:core" as core;
+
+class C extends core::Object {
+  field core::String m = "";
+  synthetic constructor •() → self::C
+    : super core::Object::•()
+    ;
+  set setter(core::String v) → void {}
+  operator []=(core::int index, core::String value) → void {}
+}
+extension _extension#0 on self::C? {
+  operator []= = self::_extension#0|[]=;
+  set setter = self::_extension#0|set#setter;
+}
+static method _extension#0|set#setter(final self::C? #this, core::String v) → void {
+  let final self::C? #t1 = #this in #t1.{core::Object::==}(null) ?{core::String?} null : #t1{self::C}.{self::C::m} = v;
+}
+static method _extension#0|[]=(final self::C? #this, core::int index, core::String value) → void {
+  let final self::C? #t2 = #this in #t2.{core::Object::==}(null) ?{core::String?} null : #t2{self::C}.{self::C::m} = "${index}${value}";
+}
+static method main() → dynamic {
+  self::C? c = new self::C::•();
+  self::expect("", let final self::C? #t3 = c in #t3.{core::Object::==}(null) ?{core::String?} null : #t3{self::C}.{self::C::m});
+  self::_extension#0|set#setter(c, "42");
+  self::expect("42", let final self::C? #t4 = c in #t4.{core::Object::==}(null) ?{core::String?} null : #t4{self::C}.{self::C::m});
+  self::_extension#0|[]=(c, 42, "87");
+  self::expect("4287", let final self::C? #t5 = c in #t5.{core::Object::==}(null) ?{core::String?} null : #t5{self::C}.{self::C::m});
+}
+static method expect(dynamic expected, dynamic actual) → dynamic {
+  if(!expected.{core::Object::==}(actual))
+    throw "Expected ${expected}, actual ${actual}";
+}
diff --git a/pkg/front_end/testcases/nnbd/nullable_setter.dart.textual_outline.expect b/pkg/front_end/testcases/nnbd/nullable_setter.dart.textual_outline.expect
new file mode 100644
index 000000000000..c1aeb83f8172
--- /dev/null
+++ b/pkg/front_end/testcases/nnbd/nullable_setter.dart.textual_outline.expect
@@ -0,0 +1,10 @@
+class C {
+  String m = "";
+  void set setter(String v) { }
+  void operator []=(int index, String value) { }
+}
+extension on ;
+C;
+? { void set setter(String v) { this?.m = v; } void operator []=(int index, String value) { this?.m = '$index$value'; } }
+main() { }
+expect(expected, actual) { }
diff --git a/pkg/front_end/testcases/nnbd/nullable_setter.dart.weak.expect b/pkg/front_end/testcases/nnbd/nullable_setter.dart.weak.expect
new file mode 100644
index 000000000000..d36785469a17
--- /dev/null
+++ b/pkg/front_end/testcases/nnbd/nullable_setter.dart.weak.expect
@@ -0,0 +1,34 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:core" as core;
+
+class C extends core::Object {
+  field core::String m = "";
+  synthetic constructor •() → self::C
+    : super core::Object::•()
+    ;
+  set setter(core::String v) → void {}
+  operator []=(core::int index, core::String value) → void {}
+}
+extension _extension#0 on self::C? {
+  operator []= = self::_extension#0|[]=;
+  set setter = self::_extension#0|set#setter;
+}
+static method _extension#0|set#setter(final self::C? #this, core::String v) → void {
+  let final self::C? #t1 = #this in #t1.{core::Object::==}(null) ?{core::String?} null : #t1{self::C}.{self::C::m} = v;
+}
+static method _extension#0|[]=(final self::C? #this, core::int index, core::String value) → void {
+  let final self::C? #t2 = #this in #t2.{core::Object::==}(null) ?{core::String?} null : #t2{self::C}.{self::C::m} = "${index}${value}";
+}
+static method main() → dynamic {
+  self::C? c = new self::C::•();
+  self::expect("", let final self::C? #t3 = c in #t3.{core::Object::==}(null) ?{core::String?} null : #t3{self::C}.{self::C::m});
+  self::_extension#0|set#setter(c, "42");
+  self::expect("42", let final self::C? #t4 = c in #t4.{core::Object::==}(null) ?{core::String?} null : #t4{self::C}.{self::C::m});
+  self::_extension#0|[]=(c, 42, "87");
+  self::expect("4287", let final self::C? #t5 = c in #t5.{core::Object::==}(null) ?{core::String?} null : #t5{self::C}.{self::C::m});
+}
+static method expect(dynamic expected, dynamic actual) → dynamic {
+  if(!expected.{core::Object::==}(actual))
+    throw "Expected ${expected}, actual ${actual}";
+}
diff --git a/pkg/front_end/testcases/nnbd/nullable_setter.dart.weak.transformed.expect b/pkg/front_end/testcases/nnbd/nullable_setter.dart.weak.transformed.expect
new file mode 100644
index 000000000000..d36785469a17
--- /dev/null
+++ b/pkg/front_end/testcases/nnbd/nullable_setter.dart.weak.transformed.expect
@@ -0,0 +1,34 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:core" as core;
+
+class C extends core::Object {
+  field core::String m = "";
+  synthetic constructor •() → self::C
+    : super core::Object::•()
+    ;
+  set setter(core::String v) → void {}
+  operator []=(core::int index, core::String value) → void {}
+}
+extension _extension#0 on self::C? {
+  operator []= = self::_extension#0|[]=;
+  set setter = self::_extension#0|set#setter;
+}
+static method _extension#0|set#setter(final self::C? #this, core::String v) → void {
+  let final self::C? #t1 = #this in #t1.{core::Object::==}(null) ?{core::String?} null : #t1{self::C}.{self::C::m} = v;
+}
+static method _extension#0|[]=(final self::C? #this, core::int index, core::String value) → void {
+  let final self::C? #t2 = #this in #t2.{core::Object::==}(null) ?{core::String?} null : #t2{self::C}.{self::C::m} = "${index}${value}";
+}
+static method main() → dynamic {
+  self::C? c = new self::C::•();
+  self::expect("", let final self::C? #t3 = c in #t3.{core::Object::==}(null) ?{core::String?} null : #t3{self::C}.{self::C::m});
+  self::_extension#0|set#setter(c, "42");
+  self::expect("42", let final self::C? #t4 = c in #t4.{core::Object::==}(null) ?{core::String?} null : #t4{self::C}.{self::C::m});
+  self::_extension#0|[]=(c, 42, "87");
+  self::expect("4287", let final self::C? #t5 = c in #t5.{core::Object::==}(null) ?{core::String?} null : #t5{self::C}.{self::C::m});
+}
+static method expect(dynamic expected, dynamic actual) → dynamic {
+  if(!expected.{core::Object::==}(actual))
+    throw "Expected ${expected}, actual ${actual}";
+}