diff --git a/src/core/core-command.c b/src/core/core-command.c
index a7dc363e7..3238e7794 100644
--- a/src/core/core-command.c
+++ b/src/core/core-command.c
@@ -8170,6 +8170,8 @@ COMMAND_CALLBACK(window)
                 gui_window_resize (ptr_tree, number);
             }
         }
+        else
+            COMMAND_ERROR;
         return WEECHAT_RC_OK;
     }