diff --git a/src/threads/thread.c b/src/threads/thread.c
index 4ddee22..0a66d65 100644
--- a/src/threads/thread.c
+++ b/src/threads/thread.c
@@ -263,7 +263,10 @@ thread_unblock (struct thread *t)
 
   old_level = intr_disable ();
   ASSERT (t->status == THREAD_BLOCKED);
-  list_push_back (&ready_list, &t->elem);
+
+  /* Insert the thread back into the ready list in priority order. */
+  list_insert_ordered(&ready_list, &t->elem, priority_more, NULL);
+
   t->status = THREAD_READY;
   intr_set_level (old_level);
 }