diff --git a/twilio/rest/resources/base.py b/twilio/rest/resources/base.py
index 07e00175a3..89d14f7bb5 100644
--- a/twilio/rest/resources/base.py
+++ b/twilio/rest/resources/base.py
@@ -223,7 +223,7 @@ def load(self, entries):
             del entries["uri"]
 
         for key in entries.keys():
-            if key.startswith("date_") and isinstance(entries[key], str):
+            if key.startswith("date_") and isinstance(entries[key], string_types):
                 entries[key] = parse_rfc2822_date(entries[key])
 
         self.__dict__.update(entries)