diff --git a/sys/fs/nfs/nfs_commonsubs.c b/sys/fs/nfs/nfs_commonsubs.c
index d9f843611b31..0f6db3281026 100644
--- a/sys/fs/nfs/nfs_commonsubs.c
+++ b/sys/fs/nfs/nfs_commonsubs.c
@@ -219,7 +219,8 @@ nfsm_mbufuio(struct nfsrv_descript *nd, struct uio *uiop, int siz)
 				}
 				mbufcp = NFSMTOD(mp, caddr_t);
 				len = mbuf_len(mp);
-				KASSERT(len > 0, ("len %d", len));
+				KASSERT(len >= 0,
+				    ("len %d, corrupted mbuf?", len));
 			}
 			xfer = (left > len) ? len : left;
 #ifdef notdef