diff --git a/backend/noop/output.c b/backend/noop/output.c
index a2595eff..14ba5ed0 100644
--- a/backend/noop/output.c
+++ b/backend/noop/output.c
@@ -61,8 +61,8 @@ struct wlr_output *wlr_noop_add_output(struct wlr_backend *wlr_backend) {
 
 	strncpy(wlr_output->make, "noop", sizeof(wlr_output->make));
 	strncpy(wlr_output->model, "noop", sizeof(wlr_output->model));
-	snprintf(wlr_output->name, sizeof(wlr_output->name), "NOOP-%d",
-		wl_list_length(&backend->outputs) + 1);
+	snprintf(wlr_output->name, sizeof(wlr_output->name), "NOOP-%ld",
+		++backend->last_output_num);
 
 	wl_list_insert(&backend->outputs, &output->link);
 
diff --git a/include/backend/noop.h b/include/backend/noop.h
index 4198baad..e301eb07 100644
--- a/include/backend/noop.h
+++ b/include/backend/noop.h
@@ -8,6 +8,7 @@ struct wlr_noop_backend {
 	struct wlr_backend backend;
 	struct wl_display *display;
 	struct wl_list outputs;
+	size_t last_output_num;
 	bool started;
 };