diff --git a/kernel/mars_bio.c b/kernel/mars_bio.c
index dde4732d..87641dc7 100644
--- a/kernel/mars_bio.c
+++ b/kernel/mars_bio.c
@@ -294,6 +294,9 @@ static int bio_ref_get(struct bio_output *output, struct mref_object *mref)
 
 
 	if (!mref->ref_data) { // buffered IO.
+		if (unlikely(mref->ref_len <= 0)) {
+			goto done;
+		}
 		status = -ENOMEM;
 		mref->ref_data = brick_block_alloc(mref->ref_pos, (mref_a->alloc_len = mref->ref_len));
 		if (unlikely(!mref->ref_data)) {