diff --git a/src/transparency_gui.cpp b/src/transparency_gui.cpp
--- a/src/transparency_gui.cpp
+++ b/src/transparency_gui.cpp
@@ -126,5 +126,5 @@ static const WindowDesc _transparency_de
 
 void ShowTransparencyToolbar(void)
 {
-	AllocateWindowDescFront(&_transparency_desc, 0);
+	AllocateWindowDescFront<Window>(&_transparency_desc, 0);
 }