diff --git a/django/core/urlresolvers.py b/django/core/urlresolvers.py
index aadd290c33..78ce00511c 100644
--- a/django/core/urlresolvers.py
+++ b/django/core/urlresolvers.py
@@ -306,10 +306,8 @@ class RegexURLResolver(LocaleRegexProvider):
                         tried.append([pattern])
                 else:
                     if sub_match:
-                        sub_match_dict = dict([(smart_str(k), v) for k, v in match.groupdict().items()])
-                        sub_match_dict.update(self.default_kwargs)
-                        for k, v in sub_match.kwargs.iteritems():
-                            sub_match_dict[smart_str(k)] = v
+                        sub_match_dict = dict(match.groupdict(), **self.default_kwargs)
+                        sub_match_dict.update(sub_match.kwargs)
                         return ResolverMatch(sub_match.func, sub_match.args, sub_match_dict, sub_match.url_name, self.app_name or sub_match.app_name, [self.namespace] + sub_match.namespaces)
                     tried.append([pattern])
             raise Resolver404({'tried': tried, 'path': new_path})