diff --git a/websocket-sharp/WebSocket.cs b/websocket-sharp/WebSocket.cs
index 4aebd11f..49c1194e 100644
--- a/websocket-sharp/WebSocket.cs
+++ b/websocket-sharp/WebSocket.cs
@@ -841,6 +841,31 @@ namespace WebSocketSharp
       return checkIfAvailable (connecting, open, closing, closed, out message);
     }
 
+    private static bool checkParametersForSetCredentials (
+      string username, string password, out string message
+    )
+    {
+      message = null;
+
+      if (username.IsNullOrEmpty ())
+        return true;
+
+      if (username.Contains (':') || !username.IsText ()) {
+        message = "'username' contains an invalid character.";
+        return false;
+      }
+
+      if (password.IsNullOrEmpty ())
+        return true;
+
+      if (!password.IsText ()) {
+        message = "'password' contains an invalid character.";
+        return false;
+      }
+
+      return true;
+    }
+
     private bool checkReceivedFrame (WebSocketFrame frame, out string message)
     {
       message = null;