diff --git a/websocket/_core.py b/websocket/_core.py
index 9297bbc..34a8eaa 100644
--- a/websocket/_core.py
+++ b/websocket/_core.py
@@ -938,7 +938,8 @@ class WebSocket(object):
                 raise
 
         if not bytes:
-            self.sock.close()
+            if self.sock:
+                self.sock.close()
             self.sock = None
             self.connected = False
             raise WebSocketConnectionClosedException()