diff --git a/websocket-sharp/WebSocket.cs b/websocket-sharp/WebSocket.cs
index b463b4f5..05b77086 100644
--- a/websocket-sharp/WebSocket.cs
+++ b/websocket-sharp/WebSocket.cs
@@ -2773,6 +2773,13 @@ namespace WebSocketSharp
         return;
       }
 
+      if (cookie == null) {
+        _logger.Error ("'cookie' is null.");
+        error ("An error has occurred in setting a cookie.", null);
+
+        return;
+      }
+
       lock (_forConn) {
         if (!checkIfAvailable (true, false, false, true, out msg)) {
           _logger.Error (msg);
@@ -2781,13 +2788,6 @@ namespace WebSocketSharp
           return;
         }
 
-        if (cookie == null) {
-          _logger.Error ("'cookie' is null.");
-          error ("An error has occurred in setting a cookie.", null);
-
-          return;
-        }
-
         lock (_cookies.SyncRoot)
           _cookies.SetOrRemove (cookie);
       }