diff --git a/lib/dns/zone.c b/lib/dns/zone.c
index c0262c5190..8668937d61 100644
--- a/lib/dns/zone.c
+++ b/lib/dns/zone.c
@@ -10048,6 +10048,7 @@ cleanup:
 	}
 
 	dns_diff_clear(&_sig_diff);
+	dns_diff_clear(&post_diff);
 
 	for (i = 0; i < nkeys; i++) {
 		dst_key_free(&zone_keys[i]);