diff --git a/src/threads/synch.c b/src/threads/synch.c
index 940faa5..1246206 100644
--- a/src/threads/synch.c
+++ b/src/threads/synch.c
@@ -303,6 +303,7 @@ lock_release (struct lock *lock)
   struct list orphan_list;
   list_init (&orphan_list);
 
+  enum intr_level old_level = intr_disable ();
   /* Loop through current thread's donors, removing the ones waiting for the
      lock being released and keeping track of them (within orphan_list).
      Also identifies the highest priority donor thread among them. */
@@ -336,6 +337,7 @@ lock_release (struct lock *lock)
         list_push_back (&max_donor->donors_list, list_pop_front (&orphan_list));
     }
 
+  intr_set_level (old_level);
   /* Removal of donors to this thread may change its effective priority,
      so recalculate. */
   thread_recalculate_priority ();