diff --git a/fhem/FHEM/34_SWAP.pm b/fhem/FHEM/34_SWAP.pm
index 832946763..b8f1f49d8 100755
--- a/fhem/FHEM/34_SWAP.pm
+++ b/fhem/FHEM/34_SWAP.pm
@@ -693,6 +693,8 @@ SWAP_Parse($$)
 {
   my ($hash, $msg) = @_;
 
+  return undef if( $msg !~ m/^[\dA-F]{12,}$/ );
+
   my $dest = substr($msg, 0, 2);
   my $src = substr($msg, 2, 2);
   my $hop = substr($msg, 4, 1);