diff --git a/lib/dns/include/dns/db.h b/lib/dns/include/dns/db.h
index d6dbe768fd..11263db23f 100644
--- a/lib/dns/include/dns/db.h
+++ b/lib/dns/include/dns/db.h
@@ -364,6 +364,10 @@ dns_db_closeversion(dns_db_t *db, dns_dbversion_t **versionp,
  *
  *	'*versionp' refers to a valid version.
  *
+ *	If committing a writable version, then there must be no other
+ *	outstanding references to the version (e.g. an active rdataset
+ *	iterator).
+ *
  * Ensures:
  *
  *	*versionp == NULL