diff --git a/test/observable_test.dart b/test/observable_test.dart
index af4d9c3..3a05e2d 100644
--- a/test/observable_test.dart
+++ b/test/observable_test.dart
@@ -9,7 +9,7 @@
 
 import 'observable_test_utils.dart';
 
-main() => observableTests();
+void main() => observableTests();
 
 void observableTests() {
   // Track the subscriptions so we can clean them up in tearDown.