diff --git a/Shorewall-perl/Shorewall/Chains.pm b/Shorewall-perl/Shorewall/Chains.pm
index dc5a41258..e5cd324a1 100644
--- a/Shorewall-perl/Shorewall/Chains.pm
+++ b/Shorewall-perl/Shorewall/Chains.pm
@@ -1194,7 +1194,7 @@ sub mac_match( $ ) {
     $mac =~ s/^!// if my $invert = ( $1 ? '! ' : '');
     $mac =~ tr/-/:/;
 
-    fatal_error "Invalid MAC address ($mac)" unless $mac =~ /^(?:[0-9a-fA-f]{2}:){5}[0-9a-fA-f]{2}$/;
+    fatal_error "Invalid MAC address ($mac)" unless $mac =~ /^(?:[0-9a-fA-F]{2}:){5}[0-9a-fA-F]{2}$/;
 
     "--match mac --mac-source ${invert}$mac ";
 }