diff --git a/lib/dns/db.c b/lib/dns/db.c
index a4c2864..62f461c 100644
--- a/lib/dns/db.c
+++ b/lib/dns/db.c
@@ -860,6 +860,8 @@ dns_db_unregister(dns_dbimplementation_t **dbimp) {
 	isc_mem_put(mctx, imp, sizeof(dns_dbimplementation_t));
 	isc_mem_detach(&mctx);
 	RWUNLOCK(&implock, isc_rwlocktype_write);
+
+	*dbimp = NULL;
 }
 
 isc_result_t