diff --git a/Changes b/Changes
index ddd5bda6..463547e8 100644
--- a/Changes
+++ b/Changes
@@ -8,6 +8,7 @@
 
   * #320 DNS subroutines are redefined
   * #318 ACLs with RegExp are very slow - aggressive resolver timeouts
+  * #317 when renumbering on discover, delete likely duplicate devices
 
 2.036001 - 2017-06-22
 
diff --git a/lib/App/Netdisco/Core/Discover.pm b/lib/App/Netdisco/Core/Discover.pm
index 25e5e0f4..1cc4b73d 100644
--- a/lib/App/Netdisco/Core/Discover.pm
+++ b/lib/App/Netdisco/Core/Discover.pm
@@ -98,6 +98,12 @@ sub set_canonical_ip {
   return if $new_ip eq $old_ip;
 
   schema('netdisco')->txn_do(sub {
+    # delete target device with the same vendor and serial number
+    schema('netdisco')->resultset('Device')->search({
+      ip => $new_ip, vendor => $device->vendor, serial => $device->serial,
+    })->delete;
+
+    # if target device exists then this will die
     $device->renumber($new_ip)
       or die "cannot renumber to: $new_ip"; # rollback