diff --git a/Shorewall-perl/Shorewall/IPAddrs.pm b/Shorewall-perl/Shorewall/IPAddrs.pm
index f0195472a..b6cd5a6e4 100644
--- a/Shorewall-perl/Shorewall/IPAddrs.pm
+++ b/Shorewall-perl/Shorewall/IPAddrs.pm
@@ -134,6 +134,8 @@ sub validate_net( $$ ) {
     my ($net, $vlsm, $rest) = split( '/', $_[0], 3 );
     my $allow_name = $_[1];
 
+    $net = '' unless defined $net;
+
     fatal_error "Missing address" if $net eq '';
     fatal_error "An ipset name ($net) is not allowed in this context" if substr( $net, 0, 1 ) eq '+';