diff --git a/pymysql/connections.py b/pymysql/connections.py
index 2884cdc..3018c06 100644
--- a/pymysql/connections.py
+++ b/pymysql/connections.py
@@ -670,7 +670,7 @@ class Connection(object):
         self.client_flag = client_flag
 
         self.cursorclass = cursorclass
-        self.connect_timeout = connect_timeout
+        self.connect_timeout = connect_timeout or None
 
         self._result = None
         self._affected_rows = 0