diff --git a/yandex_connect/base.py b/yandex_connect/base.py
index 1a10aec..9b637ca 100644
--- a/yandex_connect/base.py
+++ b/yandex_connect/base.py
@@ -121,7 +121,7 @@ class YandexConnectRequest(object):
             url = '%s/' % url
 
         if data:
-            for key in data.keys():
+            for key in list(data):
                 if data[key] is None or (isinstance(data[key], dict) and not data[key]):
                     del data[key]
                     continue