diff --git a/lib/dns/zone.c b/lib/dns/zone.c
index be0865c891..c568e6a446 100644
--- a/lib/dns/zone.c
+++ b/lib/dns/zone.c
@@ -5507,8 +5507,8 @@ zone_iattach(dns_zone_t *source, dns_zone_t **target) {
 	/*
 	 * 'source' locked by caller.
 	 */
-	REQUIRE(LOCKED_ZONE(source));
 	REQUIRE(DNS_ZONE_VALID(source));
+	REQUIRE(LOCKED_ZONE(source));
 	REQUIRE(target != NULL && *target == NULL);
 	INSIST(source->irefs + isc_refcount_current(&source->erefs) > 0);
 	source->irefs++;