diff --git a/lib/src/wrappers.dart b/lib/src/wrappers.dart
index 1ff7dc1..555296d 100644
--- a/lib/src/wrappers.dart
+++ b/lib/src/wrappers.dart
@@ -449,7 +449,7 @@
 
   /// Throws an [UnsupportedError] since there's no corresponding method for
   /// [Map]s.
-  E lookup(E element) =>
+  E lookup(Object element) =>
       throw new UnsupportedError("MapKeySet doesn't support lookup().");
 
   /// Returns a new set which contains all the elements of [this] and [other].
diff --git a/pubspec.yaml b/pubspec.yaml
index 07cb622..5d88529 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: collection
-version: 1.14.2
+version: 1.14.3
 author: Dart Team <misc@dartlang.org>
 description: Collections and utilities functions and classes related to collections.
 homepage: https://www.github.com/dart-lang/collection