diff --git a/sys/fs/nfs/nfs_commonkrpc.c b/sys/fs/nfs/nfs_commonkrpc.c
index daf8082fa1c3..6e766abcf4b1 100644
--- a/sys/fs/nfs/nfs_commonkrpc.c
+++ b/sys/fs/nfs/nfs_commonkrpc.c
@@ -871,7 +871,7 @@ newnfs_request(struct nfsrv_descript *nd, struct nfsmount *nmp,
 			sep->nfsess_slotseq[nd->nd_slotid] += 10;
 			mtx_unlock(&sep->nfsess_mtx);
 			/* And free the slot. */
-			nfsv4_freeslot(sep, nd->nd_slotid);
+			nfsv4_freeslot(sep, nd->nd_slotid, false);
 		}
 		NFSINCRGLOBAL(nfsstatsv1.rpcinvalid);
 		error = ENXIO;
@@ -1108,7 +1108,7 @@ newnfs_request(struct nfsrv_descript *nd, struct nfsmount *nmp,
 		if ((nd->nd_flag & ND_NFSV4) != 0) {
 			/* Free the slot, as required. */
 			if (freeslot != -1)
-				nfsv4_freeslot(sep, freeslot);
+				nfsv4_freeslot(sep, freeslot, false);
 			/*
 			 * If this op is Putfh, throw its results away.
 			 */
diff --git a/sys/fs/nfs/nfs_commonsubs.c b/sys/fs/nfs/nfs_commonsubs.c
index a30ee458e06c..539cbbbde7d2 100644
--- a/sys/fs/nfs/nfs_commonsubs.c
+++ b/sys/fs/nfs/nfs_commonsubs.c
@@ -4811,7 +4811,7 @@ nfsv4_sequencelookup(struct nfsmount *nmp, struct nfsclsession *sep,
  * Free a session slot.
  */
 void
-nfsv4_freeslot(struct nfsclsession *sep, int slot)
+nfsv4_freeslot(struct nfsclsession *sep, int slot, bool resetseq)
 {
 	uint64_t bitval;
 
@@ -4819,6 +4819,8 @@ nfsv4_freeslot(struct nfsclsession *sep, int slot)
 	if (slot > 0)
 		bitval <<= slot;
 	mtx_lock(&sep->nfsess_mtx);
+	if (resetseq)
+		sep->nfsess_slotseq[slot]--;
 	if ((bitval & sep->nfsess_slots) == 0)
 		printf("freeing free slot!!\n");
 	sep->nfsess_slots &= ~bitval;
diff --git a/sys/fs/nfs/nfs_var.h b/sys/fs/nfs/nfs_var.h
index 201c5a5fc2b5..f23d56050449 100644
--- a/sys/fs/nfs/nfs_var.h
+++ b/sys/fs/nfs/nfs_var.h
@@ -355,7 +355,7 @@ void nfsv4_setsequence(struct nfsmount *, struct nfsrv_descript *,
     struct nfsclsession *, int);
 int nfsv4_sequencelookup(struct nfsmount *, struct nfsclsession *, int *,
     int *, uint32_t *, uint8_t *);
-void nfsv4_freeslot(struct nfsclsession *, int);
+void nfsv4_freeslot(struct nfsclsession *, int, bool);
 struct ucred *nfsrv_getgrpscred(struct ucred *);
 struct nfsdevice *nfsv4_findmirror(struct nfsmount *);
 void nfsm_set(struct nfsrv_descript *, u_int);
diff --git a/sys/fs/nfsserver/nfs_nfsdstate.c b/sys/fs/nfsserver/nfs_nfsdstate.c
index 430f09844b83..3aebddad0962 100644
--- a/sys/fs/nfsserver/nfs_nfsdstate.c
+++ b/sys/fs/nfsserver/nfs_nfsdstate.c
@@ -4572,7 +4572,8 @@ nfsrv_docallback(struct nfsclient *clp, int procnum, nfsv4stateid_t *stateidp,
 		if ((clp->lc_flags & LCL_NFSV41) != 0) {
 			error = ECONNREFUSED;
 			if (procnum != NFSV4PROC_CBNULL)
-				nfsv4_freeslot(&sep->sess_cbsess, slotpos);
+				nfsv4_freeslot(&sep->sess_cbsess, slotpos,
+				    true);
 			nfsrv_freesession(sep, NULL);
 		} else if (nd->nd_procnum == NFSV4PROC_CBNULL)
 			error = newnfs_connect(NULL, &clp->lc_req, cred,
@@ -4604,8 +4605,24 @@ nfsrv_docallback(struct nfsclient *clp, int procnum, nfsv4stateid_t *stateidp,
 				error = ECONNREFUSED;
 			}
 			NFSD_DEBUG(4, "aft newnfs_request=%d\n", error);
-			if (error != 0 && procnum != NFSV4PROC_CBNULL)
-				nfsv4_freeslot(&sep->sess_cbsess, slotpos);
+			if (error != 0 && procnum != NFSV4PROC_CBNULL) {
+				/*
+				 * It is likely that the callback was never
+				 * processed by the client and, as such,
+				 * the sequence# for the session slot needs
+				 * to be backed up by one to avoid a
+				 * NFSERR_SEQMISORDERED error reply.
+				 * For the unlikely case where the callback
+				 * was processed by the client, this will
+				 * make the next callback on the slot
+				 * appear to be a retry.
+				 * Since callbacks never specify that the
+				 * reply be cached, this "apparent retry"
+				 * should not be a problem.
+				 */
+				nfsv4_freeslot(&sep->sess_cbsess, slotpos,
+				    true);
+			}
 			nfsrv_freesession(sep, NULL);
 		} else
 			error = newnfs_request(nd, NULL, clp, &clp->lc_req,