diff --git a/gdk/x11/gdkwindow-x11.c b/gdk/x11/gdkwindow-x11.c
index ac2a1b1c72..796c082f14 100644
--- a/gdk/x11/gdkwindow-x11.c
+++ b/gdk/x11/gdkwindow-x11.c
@@ -3725,7 +3725,7 @@ void
 gdk_x11_window_set_theme_variant (GdkWindow *window,
                                   char      *variant)
 {
-  return gdk_x11_window_set_utf8_property (window, "_GTK_THEME_VARIANT", variant);
+  gdk_x11_window_set_utf8_property (window, "_GTK_THEME_VARIANT", variant);
 }
 
 #define GDK_SELECTION_MAX_SIZE(display)                                 \