diff --git a/polygon/rest/models/definitions.py b/polygon/rest/models/definitions.py
index dbcab997..cdf443f0 100644
--- a/polygon/rest/models/definitions.py
+++ b/polygon/rest/models/definitions.py
@@ -46,7 +46,7 @@ def _unmarshal_json_object(self, input_json):
                             model = models.name_to_class[attribute_type]()
                             value = model.unmarshal_json(input_json[key])
             else:
-                attribute_name = key + "_" if keyword.iskeyword(key) else ""
+                attribute_name = key + ('_' if keyword.iskeyword(key) else '')
 
             self.__setattr__(attribute_name, value)
         return self