diff --git a/DevExpress.Mvvm.UI/Services/WindowService.cs b/DevExpress.Mvvm.UI/Services/WindowService.cs
index 5337e9b..fde99c1 100644
--- a/DevExpress.Mvvm.UI/Services/WindowService.cs
+++ b/DevExpress.Mvvm.UI/Services/WindowService.cs
@@ -34,7 +34,7 @@ static Type GetWindowType(Style windowStyle, Type expectedType) {
             return null;
         }
 
-        const string WindowTypeException = "WindowType show be derived from the Window type";
+        const string WindowTypeException = "WindowType should be derived from the Window type.";
 
         public static readonly DependencyProperty WindowStartupLocationProperty =
             DependencyProperty.Register("WindowStartupLocation", typeof(WindowStartupLocation), typeof(WindowService),