Oops, broke dart2js. (Will be included in 0.3.9.)
diff --git a/lib/src/protobuf/mixins/map_mixin.dart b/lib/src/protobuf/mixins/map_mixin.dart
index 9300640..ab593e9 100644
--- a/lib/src/protobuf/mixins/map_mixin.dart
+++ b/lib/src/protobuf/mixins/map_mixin.dart
@@ -11,7 +11,7 @@
///
/// This mixin is enabled via an option in
/// dart_options.proto in dart-protoc-plugin.
-abstract class PbMapMixin implements Map<String, dynamic> {
+abstract class PbMapMixin implements Map {
// GeneratedMessage properties and methods used by this mixin.
