diff --git a/websocket-sharp/WebSocket.cs b/websocket-sharp/WebSocket.cs
index 04a70ac7..648a5c39 100644
--- a/websocket-sharp/WebSocket.cs
+++ b/websocket-sharp/WebSocket.cs
@@ -311,8 +311,8 @@ namespace WebSocketSharp
 
       set {
         lock (_forConn) {
-          var msg = checkIfAvailable (true, false, true, false, false, true);
-          if (msg != null) {
+          string msg;
+          if (!checkIfAvailable (true, false, true, false, false, true, out msg)) {
             _logger.Error (msg);
             error ("An error has occurred in setting the compression.", null);