diff --git a/lib/dns/db.c b/lib/dns/db.c
index 577b71fa90..11e498adfd 100644
--- a/lib/dns/db.c
+++ b/lib/dns/db.c
@@ -406,6 +406,7 @@ dns_db_addrdataset(dns_db_t *db, dns_dbnode_t *node, dns_dbversion_t *version,
 		((db->attributes & DNS_DBATTR_CACHE) != 0 && version == NULL));
 	REQUIRE(DNS_RDATASET_VALID(rdataset));
 	REQUIRE(rdataset->methods != NULL);
+	REQUIRE(rdataset->rdclass == db->rdclass);
 
 	return ((db->methods->addrdataset)(db, node, version, now, rdataset));
 }
diff --git a/lib/dns/include/dns/db.h b/lib/dns/include/dns/db.h
index 38040f2849..3b7b5c1d61 100644
--- a/lib/dns/include/dns/db.h
+++ b/lib/dns/include/dns/db.h
@@ -770,7 +770,8 @@ dns_db_addrdataset(dns_db_t *db, dns_dbnode_t *node, dns_dbversion_t *version,
  *
  *	'node' is a valid node.
  *
- *	'rdataset' is a valid, associated rdataset.
+ *	'rdataset' is a valid, associated rdataset with the same class
+ *	as 'db'.
  *
  *	The database has zone semantics and 'version' is a valid
  *	read-write version, or the database has cache semantics