diff --git a/src/MaterialDesignThemes.Wpf/Themes/MaterialDesignTheme.PopupBox.xaml b/src/MaterialDesignThemes.Wpf/Themes/MaterialDesignTheme.PopupBox.xaml
index 87a1323164..31a116ee5e 100644
--- a/src/MaterialDesignThemes.Wpf/Themes/MaterialDesignTheme.PopupBox.xaml
+++ b/src/MaterialDesignThemes.Wpf/Themes/MaterialDesignTheme.PopupBox.xaml
@@ -80,6 +80,7 @@
+