diff --git a/websocket/__init__.py b/websocket/__init__.py
index d045234..3e12cbf 100644
--- a/websocket/__init__.py
+++ b/websocket/__init__.py
@@ -927,7 +927,7 @@ class WebSocketApp(object):
             if set to 0, not send automatically.
         ping_timeout: timeout(second) if the pong message is not recieved.
         """
-        if ping_timeout<=0:
+        if not ping_timeout or ping_timeout<=0:
             ping_timeout = None
         if sockopt is None:
             sockopt = []