diff --git a/pkg/dart_messages/analysis_options.yaml b/pkg/dart_messages/analysis_options.yaml
new file mode 100644
index 00000000000..a10d4c5a05c
--- /dev/null
+++ b/pkg/dart_messages/analysis_options.yaml
@@ -0,0 +1,2 @@
+analyzer:
+  strong-mode: true
diff --git a/pkg/dart_messages/bin/message_id.dart b/pkg/dart_messages/bin/message_id.dart
index 7d59fbd18a1..a708e60a51f 100644
--- a/pkg/dart_messages/bin/message_id.dart
+++ b/pkg/dart_messages/bin/message_id.dart
@@ -4,7 +4,7 @@
 
 import 'dart:math' as math;
 
-import '../lib/shared_messages.dart' as shared_messages;
+import 'package:dart_messages/shared_messages.dart' as shared_messages;
 
 math.Random random = new math.Random();
 
@@ -13,7 +13,7 @@ final $A = "A".codeUnitAt(0);
 final $Z = "Z".codeUnitAt(0);
 
 String computeId() {
-  List charCodes = [];
+  List<int> charCodes = [];
   for (int i = 0; i < idLength; i++) {
     charCodes.add($A + random.nextInt($Z - $A));
   }
diff --git a/pkg/dart_messages/bin/publish.dart b/pkg/dart_messages/bin/publish.dart
index 6ece7949683..cf4ac903c8b 100644
--- a/pkg/dart_messages/bin/publish.dart
+++ b/pkg/dart_messages/bin/publish.dart
@@ -5,7 +5,7 @@
 import 'dart:convert';
 import 'dart:io' as io;
 
-import '../lib/shared_messages.dart';
+import 'package:dart_messages/shared_messages.dart';
 
 const String jsonPath = '../lib/generated/shared_messages.json';
 const String dart2jsPath =
diff --git a/pkg/dart_messages/test/dart_messages_test.dart b/pkg/dart_messages/test/dart_messages_test.dart
index 8bc4a868634..c031857957c 100644
--- a/pkg/dart_messages/test/dart_messages_test.dart
+++ b/pkg/dart_messages/test/dart_messages_test.dart
@@ -4,7 +4,7 @@
 
 import 'dart:io' as io;
 
-import '../lib/shared_messages.dart';
+import 'package:dart_messages/shared_messages.dart';
 
 void testJsonIsUpdated() {
   var packageRoot = io.Platform.packageRoot;