diff --git a/backend/x11/output.c b/backend/x11/output.c
index 05df7984..ce90ea5e 100644
--- a/backend/x11/output.c
+++ b/backend/x11/output.c
@@ -146,8 +146,8 @@ struct wlr_output *wlr_x11_output_create(struct wlr_backend *backend) {
 
 	output_set_refresh(&output->wlr_output, 0);
 
-	snprintf(wlr_output->name, sizeof(wlr_output->name), "X11-%d",
-		wl_list_length(&x11->outputs) + 1);
+	snprintf(wlr_output->name, sizeof(wlr_output->name), "X11-%ld",
+		++x11->last_output_num);
 	parse_xcb_setup(wlr_output, x11->xcb);
 
 	uint32_t mask = XCB_CW_EVENT_MASK;
diff --git a/include/backend/x11.h b/include/backend/x11.h
index 1a8341f6..67511602 100644
--- a/include/backend/x11.h
+++ b/include/backend/x11.h
@@ -47,6 +47,7 @@ struct wlr_x11_backend {
 	xcb_screen_t *screen;
 
 	size_t requested_outputs;
+	size_t last_output_num;
 	struct wl_list outputs; // wlr_x11_output::link
 
 	struct wlr_keyboard keyboard;