diff --git a/src/main_gui.cpp b/src/main_gui.cpp
--- a/src/main_gui.cpp
+++ b/src/main_gui.cpp
@@ -2341,7 +2341,7 @@ static void MainWindowWndProc(Window *w,
 			case '6' | WKC_CTRL:
 			case '7' | WKC_CTRL:
 				/* Transparency toggle hot keys */
-				TOGGLEBIT(_transparent_opt, e->we.keypress.key - '1');
+				TOGGLEBIT(_transparent_opt, e->we.keypress.keycode - ('1' | WKC_CTRL));
 				MarkWholeScreenDirty();
 				break;