diff --git a/rest_framework/filters.py b/rest_framework/filters.py
index d57f7a8bf..734d3e8c5 100644
--- a/rest_framework/filters.py
+++ b/rest_framework/filters.py
@@ -207,9 +207,10 @@ class OrderingFilter(BaseFilterBackend):
         return self.get_default_ordering(view)
 
     def convert_to_origin_filed_name(self, request, queryset, view, ordering):
-        valid_fields = dict(self.get_valid_fields(queryset, view, {'request': request}))
+        valid_fields = self.get_valid_fields(queryset, view, {'request': request})
         if valid_fields is None or valid_fields == '__all__':
             return ordering
+        valid_fields = dict(valid_fields)
         converted_fields = []
         for field in ordering:
             if field.startswith('-'):