diff --git a/tools/perf/ui/hist.c b/tools/perf/ui/hist.c
index 6ee6b36bbc763c7546ec2f81379b31b503c577dd..db79017a6e56fc1b836fbbeb178e9eb7c57a7a89 100644
--- a/tools/perf/ui/hist.c
+++ b/tools/perf/ui/hist.c
@@ -606,6 +606,13 @@ void perf_hpp__append_sort_keys(struct perf_hpp_list *list)
 
 static void fmt_free(struct perf_hpp_fmt *fmt)
 {
+	/*
+	 * At this point fmt should be completely
+	 * unhooked, if not it's a bug.
+	 */
+	BUG_ON(!list_empty(&fmt->list));
+	BUG_ON(!list_empty(&fmt->sort_list));
+
 	if (fmt->free)
 		fmt->free(fmt);
 }