diff --git a/gen_wrap.py b/gen_wrap.py
index 17c0e896587658f9003b86f18ea81a97760b5684..86f135dcb46dcbe349fbe9dedd6abf2970fb7c6f 100644
--- a/gen_wrap.py
+++ b/gen_wrap.py
@@ -1297,7 +1297,8 @@ def write_method_wrapper(gen, cls_name, meth):
             post_call("_str_ret = None")
 
         if PY3:
-            ret_vals.insert(0, "_str_ret.decode()")
+            ret_vals.insert(0,
+                    "_str_ret.decode() if _str_ret is not None else _str_ret")
         else:
             ret_vals.insert(0, "_str_ret")