diff --git a/doc/Changelog b/doc/Changelog
index 950390980..452e4d31b 100644
--- a/doc/Changelog
+++ b/doc/Changelog
@@ -1,6 +1,8 @@
 20 April 2018: Wouter
 	- man page documentation for dns-over-tls forward-addr '#' notation.
 	- removed free from failed parse case.
+	- Fix #4091: Fix that reload of auth-zone does not merge the zonefile
+	  with the previous contents.
 
 19 April 2018: Wouter
 	- Can set tls authentication with forward-addr: IP#tls.auth.name
diff --git a/services/authzone.c b/services/authzone.c
index a7141a1ef..56c4065a4 100644
--- a/services/authzone.c
+++ b/services/authzone.c
@@ -1560,6 +1560,11 @@ auth_zone_read_zonefile(struct auth_zone* z)
 		free(n);
 		return 0;
 	}
+
+	/* clear the data tree */
+	traverse_postorder(&z->data, auth_data_del, NULL);
+	rbtree_init(&z->data, &auth_data_cmp);
+
 	memset(&state, 0, sizeof(state));
 	/* default TTL to 3600 */
 	state.default_ttl = 3600;