diff --git a/sys/fs/nfsclient/nfs_clrpcops.c b/sys/fs/nfsclient/nfs_clrpcops.c
index 23cc47f5c69..c135f3254f6 100644
--- a/sys/fs/nfsclient/nfs_clrpcops.c
+++ b/sys/fs/nfsclient/nfs_clrpcops.c
@@ -4672,8 +4672,14 @@ nfsrpc_createsession(struct nfsmount *nmp, struct nfsclsession *sep,
 	uint32_t crflags, maxval, *tl;
 	struct nfsrv_descript nfsd;
 	struct nfsrv_descript *nd = &nfsd;
-	int error, irdcnt;
+	int error, irdcnt, rsiz, wsiz;
 
+	rsiz = nmp->nm_rsize;
+	if (rsiz == 0)
+		rsiz = NFS_MAXBSIZE;
+	wsiz = nmp->nm_wsize;
+	if (wsiz == 0)
+		wsiz = NFS_MAXBSIZE;
 	nfscl_reqstart(nd, NFSPROC_CREATESESSION, nmp, NULL, 0, NULL, NULL);
 	NFSM_BUILD(tl, uint32_t *, 4 * NFSX_UNSIGNED);
 	*tl++ = sep->nfsess_clientid.lval[0];
@@ -4687,8 +4693,8 @@ nfsrpc_createsession(struct nfsmount *nmp, struct nfsclsession *sep,
 	/* Fill in fore channel attributes. */
 	NFSM_BUILD(tl, uint32_t *, 7 * NFSX_UNSIGNED);
 	*tl++ = 0;				/* Header pad size */
-	*tl++ = txdr_unsigned(nmp->nm_wsize + NFS_MAXXDR);/* Max request size */
-	*tl++ = txdr_unsigned(nmp->nm_rsize + NFS_MAXXDR);/* Max reply size */
+	*tl++ = txdr_unsigned(wsiz + NFS_MAXXDR);/* Max request size */
+	*tl++ = txdr_unsigned(rsiz + NFS_MAXXDR);/* Max reply size */
 	*tl++ = txdr_unsigned(4096);		/* Max response size cached */
 	*tl++ = txdr_unsigned(20);		/* Max operations */
 	*tl++ = txdr_unsigned(64);		/* Max slots */