diff --git a/Stylet/MessageBox.cs b/Stylet/MessageBox.cs
index bfbf3f4..c0bd904 100644
--- a/Stylet/MessageBox.cs
+++ b/Stylet/MessageBox.cs
@@ -25,7 +25,7 @@ namespace Stylet
         /// <param name="options">Additional options</param>
         /// <param name="buttonLabels">You may override the text for individual buttons on a case-by-case basis</param>
         /// <returns>Which button the user clicked</returns>
-        public static MessageBoxResult ShowMessageBox(this IWindowManager windowManager, string text, string title = null,
+        public static MessageBoxResult ShowMessageBox(this IWindowManager windowManager, string text, string title = "",
             MessageBoxButton buttons = MessageBoxButton.OK, MessageBoxImage icon = MessageBoxImage.None,
             MessageBoxResult defaultButton = MessageBoxResult.None, MessageBoxResult cancelButton = MessageBoxResult.None,
             MessageBoxOptions options = MessageBoxOptions.None,