diff --git a/Changes b/Changes
index e6338399..ced54f5a 100644
--- a/Changes
+++ b/Changes
@@ -6,6 +6,7 @@
 
   [BUG FIXES]
 
+  * #722 manual topology should not allow same left and right port/device
   * #729 Discovery partially fails on invalid indexes
 
 2.045007 - 2020-06-05
diff --git a/lib/App/Netdisco/Web/Plugin/AdminTask/Topology.pm b/lib/App/Netdisco/Web/Plugin/AdminTask/Topology.pm
index 746d22bc..f4b0b7d7 100644
--- a/lib/App/Netdisco/Web/Plugin/AdminTask/Topology.pm
+++ b/lib/App/Netdisco/Web/Plugin/AdminTask/Topology.pm
@@ -26,6 +26,9 @@ sub _sanity_ok {
     return 0 unless param('port1');
     return 0 unless param('port2');
 
+    return 0 if
+      (($dev1->addr eq $dev2->addr) and (param('port1') eq param('port2')));
+
     return 1;
 }