diff --git a/html/cgi-bin/firewall.cgi b/html/cgi-bin/firewall.cgi
index 1483e779f..532f99f91 100644
--- a/html/cgi-bin/firewall.cgi
+++ b/html/cgi-bin/firewall.cgi
@@ -1552,6 +1552,11 @@ sub newrule
 				$fwdfwsettings{'USE_NAT'}				= $hash{$key}[28];
 				$fwdfwsettings{'nat'}					= $hash{$key}[31]; #changed order
 				$fwdfwsettings{$fwdfwsettings{'nat'}}	= $hash{$key}[29];
+				#Fix BUG 12479
+				#When copying a DNAT Rule, the sourceport has to be empty at this point.
+				if($hash{$key}[14] eq 'cust_srv' and $hash{$key}[31] eq 'dnat'){
+					$hash{$key}[30] = '';
+				}
 				$fwdfwsettings{'dnatport'}				= $hash{$key}[30];
 				$fwdfwsettings{'LIMIT_CON_CON'}			= $hash{$key}[32];
 				$fwdfwsettings{'concon'}				= $hash{$key}[33];