diff --git a/lib/dns/include/dns/xfrin.h b/lib/dns/include/dns/xfrin.h
index f140c534ac..3d10bb42fe 100644
--- a/lib/dns/include/dns/xfrin.h
+++ b/lib/dns/include/dns/xfrin.h
@@ -125,8 +125,8 @@ dns_xfrin_getendserial(const dns_xfrin_t *xfr);
  */
 
 void
-dns_xfrin_getstats(const dns_xfrin_t *xfr, unsigned int *nmsgp,
-		   unsigned int *nrecsp, uint64_t *nbytesp);
+dns_xfrin_getstats(dns_xfrin_t *xfr, unsigned int *nmsgp, unsigned int *nrecsp,
+		   uint64_t *nbytesp);
 /*%<
  * Get various statistics values of the xfrin object: number of the received
  * messages, number of the received records, number of the received bytes.
diff --git a/lib/dns/xfrin.c b/lib/dns/xfrin.c
index 23de072e0e..c830533a27 100644
--- a/lib/dns/xfrin.c
+++ b/lib/dns/xfrin.c
@@ -16,6 +16,7 @@
 #include <inttypes.h>
 #include <stdbool.h>
 
+#include <isc/atomic.h>
 #include <isc/mem.h>
 #include <isc/random.h>
 #include <isc/result.h>
@@ -140,11 +141,14 @@ struct dns_xfrin {
 	dns_diff_t diff; /*%< Pending database changes */
 	int difflen;	 /*%< Number of pending tuples */
 
-	xfrin_state_t state;
+	_Atomic xfrin_state_t state;
 	uint32_t end_serial;
 	uint32_t expireopt;
-	bool edns, is_ixfr, expireoptset;
+	bool edns, expireoptset;
+	atomic_bool is_ixfr;
 
+	isc_mutex_t statslock;
+	/* Locked by statslock.  */
 	unsigned int nmsg;  /*%< Number of messages recvd */
 	unsigned int nrecs; /*%< Number of records recvd */
 	uint64_t nbytes;    /*%< Number of bytes received */
@@ -269,7 +273,7 @@ static isc_result_t
 axfr_init(dns_xfrin_t *xfr) {
 	isc_result_t result;
 
-	xfr->is_ixfr = false;
+	atomic_store(&xfr->is_ixfr, false);
 
 	if (xfr->db != NULL) {
 		dns_db_detach(&xfr->db);
@@ -385,7 +389,7 @@ ixfr_init(dns_xfrin_t *xfr) {
 		return (DNS_R_FORMERR);
 	}
 
-	xfr->is_ixfr = true;
+	atomic_store(&xfr->is_ixfr, true);
 	INSIST(xfr->db != NULL);
 	xfr->difflen = 0;
 
@@ -491,7 +495,9 @@ static isc_result_t
 xfr_rr(dns_xfrin_t *xfr, dns_name_t *name, uint32_t ttl, dns_rdata_t *rdata) {
 	isc_result_t result;
 
+	LOCK(&xfr->statslock);
 	xfr->nrecs++;
+	UNLOCK(&xfr->statslock);
 
 	if (rdata->type == dns_rdatatype_none ||
 	    dns_rdatatype_ismeta(rdata->type))
@@ -519,7 +525,7 @@ xfr_rr(dns_xfrin_t *xfr, dns_name_t *name, uint32_t ttl, dns_rdata_t *rdata) {
 	}
 
 redo:
-	switch (xfr->state) {
+	switch (atomic_load(&xfr->state)) {
 	case XFRST_SOAQUERY:
 		if (rdata->type != dns_rdatatype_soa) {
 			xfrin_log(xfr, ISC_LOG_NOTICE,
@@ -536,7 +542,7 @@ redo:
 				  xfr->ixfr.request_serial, xfr->end_serial);
 			FAIL(DNS_R_UPTODATE);
 		}
-		xfr->state = XFRST_GOTSOA;
+		atomic_store(&xfr->state, XFRST_GOTSOA);
 		break;
 
 	case XFRST_GOTSOA:
@@ -578,7 +584,7 @@ redo:
 		xfr->firstsoa_data = isc_mem_allocate(xfr->mctx, rdata->length);
 		memcpy(xfr->firstsoa_data, rdata->data, rdata->length);
 		xfr->firstsoa.data = xfr->firstsoa_data;
-		xfr->state = XFRST_FIRSTDATA;
+		atomic_store(&xfr->state, XFRST_FIRSTDATA);
 		break;
 
 	case XFRST_FIRSTDATA:
@@ -593,25 +599,25 @@ redo:
 			xfrin_log(xfr, ISC_LOG_DEBUG(3),
 				  "got incremental response");
 			CHECK(ixfr_init(xfr));
-			xfr->state = XFRST_IXFR_DELSOA;
+			atomic_store(&xfr->state, XFRST_IXFR_DELSOA);
 		} else {
 			xfrin_log(xfr, ISC_LOG_DEBUG(3),
 				  "got nonincremental response");
 			CHECK(axfr_init(xfr));
-			xfr->state = XFRST_AXFR;
+			atomic_store(&xfr->state, XFRST_AXFR);
 		}
 		goto redo;
 
 	case XFRST_IXFR_DELSOA:
 		INSIST(rdata->type == dns_rdatatype_soa);
 		CHECK(ixfr_putdata(xfr, DNS_DIFFOP_DEL, name, ttl, rdata));
-		xfr->state = XFRST_IXFR_DEL;
+		atomic_store(&xfr->state, XFRST_IXFR_DEL);
 		break;
 
 	case XFRST_IXFR_DEL:
 		if (rdata->type == dns_rdatatype_soa) {
 			uint32_t soa_serial = dns_soa_getserial(rdata);
-			xfr->state = XFRST_IXFR_ADDSOA;
+			atomic_store(&xfr->state, XFRST_IXFR_ADDSOA);
 			xfr->ixfr.current_serial = soa_serial;
 			goto redo;
 		}
@@ -621,7 +627,7 @@ redo:
 	case XFRST_IXFR_ADDSOA:
 		INSIST(rdata->type == dns_rdatatype_soa);
 		CHECK(ixfr_putdata(xfr, DNS_DIFFOP_ADD, name, ttl, rdata));
-		xfr->state = XFRST_IXFR_ADD;
+		atomic_store(&xfr->state, XFRST_IXFR_ADD);
 		break;
 
 	case XFRST_IXFR_ADD:
@@ -629,7 +635,7 @@ redo:
 			uint32_t soa_serial = dns_soa_getserial(rdata);
 			if (soa_serial == xfr->end_serial) {
 				CHECK(ixfr_commit(xfr));
-				xfr->state = XFRST_IXFR_END;
+				atomic_store(&xfr->state, XFRST_IXFR_END);
 				break;
 			} else if (soa_serial != xfr->ixfr.current_serial) {
 				xfrin_log(xfr, ISC_LOG_NOTICE,
@@ -639,7 +645,7 @@ redo:
 				FAIL(DNS_R_FORMERR);
 			} else {
 				CHECK(ixfr_commit(xfr));
-				xfr->state = XFRST_IXFR_DELSOA;
+				atomic_store(&xfr->state, XFRST_IXFR_DELSOA);
 				goto redo;
 			}
 		}
@@ -674,7 +680,7 @@ redo:
 				FAIL(DNS_R_FORMERR);
 			}
 			CHECK(axfr_commit(xfr));
-			xfr->state = XFRST_AXFR_END;
+			atomic_store(&xfr->state, XFRST_AXFR_END);
 			break;
 		}
 		break;
@@ -778,10 +784,10 @@ dns_xfrin_getstate(const dns_xfrin_t *xfr, const char **statestr,
 	REQUIRE(statestr != NULL && *statestr == NULL);
 	REQUIRE(is_ixfr != NULL);
 
-	state = xfr->state;
+	state = atomic_load(&xfr->state);
 	*statestr = "";
 	*is_first_data_received = (state > XFRST_FIRSTDATA);
-	*is_ixfr = xfr->is_ixfr;
+	*is_ixfr = atomic_load(&xfr->is_ixfr);
 
 	switch (state) {
 	case XFRST_SOAQUERY:
@@ -822,14 +828,16 @@ dns_xfrin_getendserial(const dns_xfrin_t *xfr) {
 }
 
 void
-dns_xfrin_getstats(const dns_xfrin_t *xfr, unsigned int *nmsgp,
-		   unsigned int *nrecsp, uint64_t *nbytesp) {
+dns_xfrin_getstats(dns_xfrin_t *xfr, unsigned int *nmsgp, unsigned int *nrecsp,
+		   uint64_t *nbytesp) {
 	REQUIRE(VALID_XFRIN(xfr));
 	REQUIRE(nmsgp != NULL && nrecsp != NULL && nbytesp != NULL);
 
+	LOCK(&xfr->statslock);
 	*nmsgp = xfr->nmsg;
 	*nrecsp = xfr->nrecs;
 	*nbytesp = xfr->nbytes;
+	UNLOCK(&xfr->statslock);
 }
 
 const isc_sockaddr_t *
@@ -925,7 +933,7 @@ xfrin_fail(dns_xfrin_t *xfr, isc_result_t result, const char *msg) {
 		{
 			xfrin_log(xfr, ISC_LOG_ERROR, "%s: %s", msg,
 				  isc_result_totext(result));
-			if (xfr->is_ixfr) {
+			if (atomic_load(&xfr->is_ixfr)) {
 				/*
 				 * Pass special result code to force AXFR retry
 				 */
@@ -979,7 +987,10 @@ xfrin_create(isc_mem_t *mctx, dns_zone_t *zone, dns_db_t *db,
 	dns_view_weakattach(dns_zone_getview(zone), &xfr->view);
 	dns_name_init(&xfr->name, NULL);
 
+	isc_mutex_init(&xfr->statslock);
+
 	atomic_init(&xfr->shuttingdown, false);
+	atomic_init(&xfr->is_ixfr, false);
 
 	if (db != NULL) {
 		dns_db_attach(db, &xfr->db);
@@ -988,9 +999,9 @@ xfrin_create(isc_mem_t *mctx, dns_zone_t *zone, dns_db_t *db,
 	dns_diff_init(xfr->mctx, &xfr->diff);
 
 	if (reqtype == dns_rdatatype_soa) {
-		xfr->state = XFRST_SOAQUERY;
+		atomic_init(&xfr->state, XFRST_SOAQUERY);
 	} else {
-		xfr->state = XFRST_INITIALSOA;
+		atomic_init(&xfr->state, XFRST_INITIALSOA);
 	}
 
 	xfr->start = isc_time_now();
@@ -1363,9 +1374,11 @@ xfrin_send_request(dns_xfrin_t *xfr) {
 		CHECK(add_opt(msg, udpsize, reqnsid, reqexpire));
 	}
 
+	LOCK(&xfr->statslock);
 	xfr->nmsg = 0;
 	xfr->nrecs = 0;
 	xfr->nbytes = 0;
+	UNLOCK(&xfr->statslock);
 	xfr->start = isc_time_now();
 	msg->id = xfr->id;
 	if (xfr->tsigctx != NULL) {
@@ -1497,9 +1510,11 @@ xfrin_recv_done(isc_result_t result, isc_region_t *region, void *arg) {
 
 	dns_message_setclass(msg, xfr->rdclass);
 
+	LOCK(&xfr->statslock);
 	if (xfr->nmsg > 0) {
 		msg->tcp_continuation = 1;
 	}
+	UNLOCK(&xfr->statslock);
 
 	isc_buffer_init(&buffer, region->base, region->length);
 	isc_buffer_add(&buffer, region->length);
@@ -1523,8 +1538,8 @@ xfrin_recv_done(isc_result_t result, isc_region_t *region, void *arg) {
 	{
 		if (result == ISC_R_SUCCESS &&
 		    msg->rcode == dns_rcode_formerr && xfr->edns &&
-		    (xfr->state == XFRST_SOAQUERY ||
-		     xfr->state == XFRST_INITIALSOA))
+		    (atomic_load(&xfr->state) == XFRST_SOAQUERY ||
+		     atomic_load(&xfr->state) == XFRST_INITIALSOA))
 		{
 			xfr->edns = false;
 			dns_message_detach(&msg);
@@ -1559,7 +1574,7 @@ xfrin_recv_done(isc_result_t result, isc_region_t *region, void *arg) {
 		dns_message_detach(&msg);
 		xfrin_reset(xfr);
 		xfr->reqtype = dns_rdatatype_soa;
-		xfr->state = XFRST_SOAQUERY;
+		atomic_store(&xfr->state, XFRST_SOAQUERY);
 	try_again:
 		result = xfrin_start(xfr);
 		if (result != ISC_R_SUCCESS) {
@@ -1583,7 +1598,8 @@ xfrin_recv_done(isc_result_t result, isc_region_t *region, void *arg) {
 		goto failure;
 	}
 
-	if ((xfr->state == XFRST_SOAQUERY || xfr->state == XFRST_INITIALSOA) &&
+	if ((atomic_load(&xfr->state) == XFRST_SOAQUERY ||
+	     atomic_load(&xfr->state) == XFRST_INITIALSOA) &&
 	    msg->counts[DNS_SECTION_QUESTION] != 1)
 	{
 		xfrin_log(xfr, ISC_LOG_NOTICE, "missing question section");
@@ -1633,7 +1649,7 @@ xfrin_recv_done(isc_result_t result, isc_region_t *region, void *arg) {
 	 * if the first RR in the answer section is not a SOA record.
 	 */
 	if (xfr->reqtype == dns_rdatatype_ixfr &&
-	    xfr->state == XFRST_INITIALSOA &&
+	    atomic_load(&xfr->state) == XFRST_INITIALSOA &&
 	    msg->counts[DNS_SECTION_ANSWER] == 0)
 	{
 		xfrin_log(xfr, ISC_LOG_DEBUG(3),
@@ -1700,24 +1716,29 @@ xfrin_recv_done(isc_result_t result, isc_region_t *region, void *arg) {
 		CHECK(dns_message_getquerytsig(msg, xfr->mctx, &xfr->lasttsig));
 	} else if (dns_message_gettsigkey(msg) != NULL) {
 		xfr->sincetsig++;
+		LOCK(&xfr->statslock);
 		if (xfr->sincetsig > 100 || xfr->nmsg == 0 ||
-		    xfr->state == XFRST_AXFR_END ||
-		    xfr->state == XFRST_IXFR_END)
+		    atomic_load(&xfr->state) == XFRST_AXFR_END ||
+		    atomic_load(&xfr->state) == XFRST_IXFR_END)
 		{
+			UNLOCK(&xfr->statslock);
 			result = DNS_R_EXPECTEDTSIG;
 			goto failure;
 		}
+		UNLOCK(&xfr->statslock);
 	}
 
 	/*
 	 * Update the number of messages received.
 	 */
+	LOCK(&xfr->statslock);
 	xfr->nmsg++;
 
 	/*
 	 * Update the number of bytes received.
 	 */
 	xfr->nbytes += buffer.used;
+	UNLOCK(&xfr->statslock);
 
 	/*
 	 * Take the context back.
@@ -1730,10 +1751,10 @@ xfrin_recv_done(isc_result_t result, isc_region_t *region, void *arg) {
 		get_edns_expire(xfr, msg);
 	}
 
-	switch (xfr->state) {
+	switch (atomic_load(&xfr->state)) {
 	case XFRST_GOTSOA:
 		xfr->reqtype = dns_rdatatype_axfr;
-		xfr->state = XFRST_INITIALSOA;
+		atomic_store(&xfr->state, XFRST_INITIALSOA);
 		CHECK(xfrin_send_request(xfr));
 		break;
 	case XFRST_AXFR_END:
@@ -1826,6 +1847,7 @@ xfrin_destroy(dns_xfrin_t *xfr) {
 	if (msecs == 0) {
 		msecs = 1;
 	}
+	LOCK(&xfr->statslock);
 	persec = (xfr->nbytes * 1000) / msecs;
 	xfrin_log(xfr, ISC_LOG_INFO,
 		  "Transfer completed: %d messages, %d records, "
@@ -1834,6 +1856,8 @@ xfrin_destroy(dns_xfrin_t *xfr) {
 		  xfr->nmsg, xfr->nrecs, xfr->nbytes,
 		  (unsigned int)(msecs / 1000), (unsigned int)(msecs % 1000),
 		  (unsigned int)persec, xfr->end_serial);
+	UNLOCK(&xfr->statslock);
+	isc_mutex_destroy(&xfr->statslock);
 
 	if (xfr->dispentry != NULL) {
 		dns_dispatch_done(&xfr->dispentry);