diff --git a/fs/nfs/callback_xdr.c b/fs/nfs/callback_xdr.c
index 56a3cc51010766ab96b77b8c52dae81d10b6b8b1..537f21da6e5f1fa9e4ed258a5bc642f3b825e0d3 100644
--- a/fs/nfs/callback_xdr.c
+++ b/fs/nfs/callback_xdr.c
@@ -521,6 +521,14 @@ static unsigned encode_cb_sequence_res(struct svc_rqst *rqstp,
 static __be32
 preprocess_nfs41_op(int nop, unsigned int op_nr, struct callback_op **op)
 {
+	if (op_nr == OP_CB_SEQUENCE) {
+		if (nop != 0)
+			return htonl(NFS4ERR_SEQUENCE_POS);
+	} else {
+		if (nop == 0)
+			return htonl(NFS4ERR_OP_NOT_IN_SESSION);
+	}
+
 	switch (op_nr) {
 	case OP_CB_GETATTR:
 	case OP_CB_RECALL: