diff --git a/fs/buffer.c b/fs/buffer.c
index 6fa5302..267e4d1 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2939,6 +2939,7 @@ static void end_bio_bh_io_sync(struct bio *bio, int err)
 	if (unlikely (test_bit(BIO_QUIET,&bio->bi_flags)))
 		set_bit(BH_Quiet, &bh->b_state);
 
+	BUG_ON(bh->b_end_io == NULL);
 	bh->b_end_io(bh, test_bit(BIO_UPTODATE, &bio->bi_flags));
 	bio_put(bio);
 }