diff --git a/src/object/pickle_support.cpp b/src/object/pickle_support.cpp
index 69a8f5a7..f70eb17f 100644
--- a/src/object/pickle_support.cpp
+++ b/src/object/pickle_support.cpp
@@ -23,7 +23,7 @@ namespace {
       if (!getattr(instance_obj, "__safe_for_unpickling__", none))
       {
           str type_name(getattr(instance_class, "__name__"));
-          str module_name(getattr(instance_class, "__module__", str()));
+          str module_name(getattr(instance_class, "__module__", object("")));
           if (module_name)
               module_name += ".";