Use full import paths for test protos.
diff --git a/proto/extensions_test.go b/proto/extensions_test.go
index 6495f56..92d1334 100644
--- a/proto/extensions_test.go
+++ b/proto/extensions_test.go
@@ -34,8 +34,8 @@
 import (
 	"testing"
 
-	pb "./testdata"
 	"github.com/golang/protobuf/proto"
+	pb "github.com/golang/protobuf/proto/testdata"
 )
 
 func TestGetExtensionsWithMissingExtensions(t *testing.T) {