diff --git a/websocket-sharp/Server/WebSocketServer.cs b/websocket-sharp/Server/WebSocketServer.cs
index 73e12119..535439ec 100644
--- a/websocket-sharp/Server/WebSocketServer.cs
+++ b/websocket-sharp/Server/WebSocketServer.cs
@@ -887,17 +887,22 @@ namespace WebSocketSharp.Server
     /// The type of the behavior of the service to add. The TBehavior must inherit
     /// the <see cref="WebSocketBehavior"/> class.
     /// </typeparam>
-    public void AddWebSocketService<TBehavior> (string path, Func<TBehavior> initializer)
+    public void AddWebSocketService<TBehavior> (
+      string path, Func<TBehavior> initializer
+    )
       where TBehavior : WebSocketBehavior
     {
-      var msg = path.CheckIfValidServicePath () ??
-                (initializer == null ? "'initializer' is null." : null);
-
-      if (msg != null) {
+      string msg;
+      if (!checkServicePath (path, out msg)) {
         _logger.Error (msg);
         return;
       }
 
+      if (initializer == null) {
+        _logger.Error ("'initializer' is null.");
+        return;
+      }
+
       _services.Add<TBehavior> (path, initializer);
     }