diff --git a/websocket-sharp/WebSocket.cs b/websocket-sharp/WebSocket.cs
index 19f68b46..4aebd11f 100644
--- a/websocket-sharp/WebSocket.cs
+++ b/websocket-sharp/WebSocket.cs
@@ -2818,32 +2818,34 @@ namespace WebSocketSharp
         return;
       }
 
-      lock (_forState) {
-        if (!checkIfAvailable (true, false, false, true, out msg)) {
-          _logger.Error (msg);
+      if (!username.IsNullOrEmpty ()) {
+        if (username.Contains (':') || !username.IsText ()) {
+          _logger.Error ("'username' contains an invalid character.");
           error ("An error has occurred in setting the credentials.", null);
 
           return;
         }
 
-        if (username.IsNullOrEmpty ()) {
-          _logger.Warn ("The credentials are set back to the default.");
-          _credentials = null;
-          _preAuth = false;
+        if (!password.IsNullOrEmpty () && !password.IsText ()) {
+          _logger.Error ("'password' contains an invalid character.");
+          error ("An error has occurred in setting the credentials.", null);
 
           return;
         }
+      }
 
-        if (username.Contains (':') || !username.IsText ()) {
-          _logger.Error ("'username' contains an invalid character.");
+      lock (_forState) {
+        if (!checkIfAvailable (true, false, false, true, out msg)) {
+          _logger.Error (msg);
           error ("An error has occurred in setting the credentials.", null);
 
           return;
         }
 
-        if (!password.IsNullOrEmpty () && !password.IsText ()) {
-          _logger.Error ("'password' contains an invalid character.");
-          error ("An error has occurred in setting the credentials.", null);
+        if (username.IsNullOrEmpty ()) {
+          _logger.Warn ("The credentials are set back to the default.");
+          _credentials = null;
+          _preAuth = false;
 
           return;
         }