diff --git a/ipc/sem.c b/ipc/sem.c
index d56d3ab..e9418df 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -1250,6 +1250,7 @@
 	undo_list = tsk->sysvsem.undo_list;
 	if (!undo_list)
 		return;
+	tsk->sysvsem.undo_list = NULL;
 
 	if (!atomic_dec_and_test(&undo_list->refcnt))
 		return;