diff --git a/proto/clone_test.go b/proto/clone_test.go
index 5e82491..c9c4a2f 100644
--- a/proto/clone_test.go
+++ b/proto/clone_test.go
@@ -32,6 +32,7 @@
 package proto_test
 
 import (
+	"log"
 	"testing"
 
 	"goprotobuf.googlecode.com/hg/proto"
@@ -56,6 +57,15 @@
 	RepBytes: [][]byte{[]byte("sham"), []byte("wow")},
 }
 
+func init() {
+	ext := &pb.Ext{
+		Data: proto.String("extension"),
+	}
+	if err := proto.SetExtension(cloneTestMessage, pb.E_Ext_More, ext); err != nil {
+		log.Fatalf("SetExtension: %v", err)
+	}
+}
+
 func TestClone(t *testing.T) {
 	m := proto.Clone(cloneTestMessage).(*pb.MyMessage)
 	if !proto.Equal(m, cloneTestMessage) {