diff --git a/src/WinUIEx/HwndExtensions.cs b/src/WinUIEx/HwndExtensions.cs
index 9c987a45..e2b5c709 100644
--- a/src/WinUIEx/HwndExtensions.cs
+++ b/src/WinUIEx/HwndExtensions.cs
@@ -302,7 +302,7 @@ public static void ToggleExtendedWindowStyle(IntPtr hWnd, bool visible, Extended
             var currentStyle = PInvoke.GetWindowLong(h, WINDOW_LONG_PTR_INDEX.GWL_EXSTYLE);
             var newStyle = currentStyle;
             if (visible)
-                newStyle = (newStyle & (int)style);
+                newStyle = (newStyle | (int)style);
             else
                 newStyle = (newStyle & ~(int)style);
             var r = PInvoke.SetWindowLong(h, WINDOW_LONG_PTR_INDEX.GWL_EXSTYLE, newStyle);