diff --git a/test/testwm.c b/test/testwm.c
index 3315aea381..c91ec59126 100644
--- a/test/testwm.c
+++ b/test/testwm.c
@@ -214,7 +214,7 @@ static void loop(void)
         if (event.type == SDL_EVENT_MOUSE_BUTTON_UP) {
             SDL_Window *window = SDL_GetMouseFocus();
             if (highlighted_mode.w && window) {
-                SDL_copyp(&state->fullscreen_mode, &highlighted_mode, sizeof(state->fullscreen_mode));
+                SDL_copyp(&state->fullscreen_mode, &highlighted_mode);
                 SDL_SetWindowFullscreenMode(window, &highlighted_mode);
             }
         }