diff --git a/ruby/tests/stress.proto b/ruby/tests/stress.proto
index 517e746..e7a0042 100644
--- a/ruby/tests/stress.proto
+++ b/ruby/tests/stress.proto
@@ -3,10 +3,10 @@
 package stress_test_protos;
 
 message TestMessage {
-  int32 a = 1;
+  optional int32 a = 1;
   repeated M b = 2;
 }
 
 message M {
-  string foo = 1;
+  optional string foo = 1;
 }