diff --git a/ipc/sem.c b/ipc/sem.c
index b93b561..d61362b 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -109,6 +109,7 @@
 	int			pid;	 /* process id of requesting process */
 	int			status;	 /* completion status of operation */
 	struct sembuf		*sops;	 /* array of pending operations */
+	struct sembuf		*blocking; /* the operation that blocked */
 	int			nsops;	 /* number of operations */
 	int			alter;	 /* does *sops alter the array? */
 };
@@ -642,6 +643,8 @@
 	goto undo;
 
 would_block:
+	q->blocking = sop;
+
 	if (sop->sem_flg & IPC_NOWAIT)
 		result = -EAGAIN;
 	else