diff --git a/objects/screen.c b/objects/screen.c
index 9ed3db96..5b701f29 100644
--- a/objects/screen.c
+++ b/objects/screen.c
@@ -1029,6 +1029,7 @@ luaA_screen_module_index(lua_State *L)
             foreach(output, (*screen)->outputs)
                 if(A_STREQ(output->name, name))
                     return luaA_object_push(L, *screen);
+        luaL_error(L, "Unknown screen output name: %s", name);
     }
 
     return luaA_object_push(L, luaA_checkscreen(L, 2));