diff --git a/CHANGES b/CHANGES
index cf2d9e4e47..7dd5d4288f 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,6 @@
+5116.	[bug]		Named/named-checkconf triggered a assertion when
+			a mirror zone's name is bad. [GL #778]
+
 5115.	[bug]		Allow unsupported algorithms in zone when not used for
 			signing with dnssec-signzone. [GL #783]
 
diff --git a/bin/tests/system/checkconf/bad-mirror-zonename.conf b/bin/tests/system/checkconf/bad-mirror-zonename.conf
new file mode 100644
index 0000000000..3c4663ec69
--- /dev/null
+++ b/bin/tests/system/checkconf/bad-mirror-zonename.conf
@@ -0,0 +1,4 @@
+zone "\0example" {
+        type mirror;
+        file "example.db";
+};
diff --git a/lib/bind9/check.c b/lib/bind9/check.c
index 2261143229..8b14d3a3cd 100644
--- a/lib/bind9/check.c
+++ b/lib/bind9/check.c
@@ -1958,7 +1958,7 @@ check_zoneconf(const cfg_obj_t *zconfig, const cfg_obj_t *voptions,
 	unsigned int i;
 	dns_rdataclass_t zclass;
 	dns_fixedname_t fixedname;
-	dns_name_t *zname = NULL;
+	dns_name_t *zname = NULL; /* NULL if parsing of zone name fails. */
 	isc_buffer_t b;
 	bool root = false;
 	bool rfc1918 = false;
@@ -1977,10 +1977,10 @@ check_zoneconf(const cfg_obj_t *zconfig, const cfg_obj_t *voptions,
 	};
 
 	static optionstable dialups[] = {
-	{ "notify", CFG_ZONE_MASTER | CFG_ZONE_SLAVE },
-	{ "notify-passive", CFG_ZONE_SLAVE },
-	{ "passive", CFG_ZONE_SLAVE | CFG_ZONE_STUB },
-	{ "refresh", CFG_ZONE_SLAVE | CFG_ZONE_STUB },
+		{ "notify", CFG_ZONE_MASTER | CFG_ZONE_SLAVE },
+		{ "notify-passive", CFG_ZONE_SLAVE },
+		{ "passive", CFG_ZONE_SLAVE | CFG_ZONE_STUB },
+		{ "refresh", CFG_ZONE_SLAVE | CFG_ZONE_STUB },
 	};
 
 	znamestr = cfg_obj_asstring(cfg_tuple_get(zconfig, "name"));
@@ -2273,7 +2273,8 @@ check_zoneconf(const cfg_obj_t *zconfig, const cfg_obj_t *voptions,
 	 * server list is used in the absence of one explicitly specified.
 	 */
 	if (ztype == CFG_ZONE_SLAVE || ztype == CFG_ZONE_STUB ||
-	    (ztype == CFG_ZONE_MIRROR && !dns_name_equal(zname, dns_rootname)))
+	    (ztype == CFG_ZONE_MIRROR && zname != NULL &&
+	     !dns_name_equal(zname, dns_rootname)))
 	{
 		obj = NULL;
 		if (cfg_map_get(zoptions, "masters", &obj) != ISC_R_SUCCESS) {
@@ -2567,7 +2568,6 @@ check_zoneconf(const cfg_obj_t *zconfig, const cfg_obj_t *voptions,
 		}
 	}
 
-
 	/*
 	 * Check that max-zone-ttl isn't used with masterfile-format map
 	 */