diff --git a/python/populse_db/database.py b/python/populse_db/database.py
index 961c39f..cfa5d42 100644
--- a/python/populse_db/database.py
+++ b/python/populse_db/database.py
@@ -1630,7 +1630,8 @@ def __check_type_value(value, valid_type):
             return True
         if valid_type == FIELD_TYPE_BOOLEAN and value_type == bool:
             return True
-        if valid_type == FIELD_TYPE_STRING and isinstance(value, str):
+        if valid_type == FIELD_TYPE_STRING and isinstance(value,
+                                                          six.string_types):
             return True
         if valid_type == FIELD_TYPE_JSON and isinstance(value, dict):
             return True