diff --git a/FHEM/10_FS20.pm b/FHEM/10_FS20.pm
index 1f17da09e..17ac851bf 100755
--- a/FHEM/10_FS20.pm
+++ b/FHEM/10_FS20.pm
@@ -145,7 +145,9 @@ Do_On_Till($@)
 
   my @b = ($a[0], "on");
   FS20_Set($hash, @b);
-  CommandDefine(undef, $hash->{NAME} . "_till at $hms_till set $a[0] off");
+  my $tname = $hash->{NAME} . "_till";
+  CommandDelete(undef, $tname) if($defs{$tname});
+  CommandDefine(undef, "$tname at $hms_till set $a[0] off");
 
 }