diff --git a/bin/slubsipbuilder.pl b/bin/slubsipbuilder.pl
index 0c64680365a0a06321f169e8963c192deaaac77a..fb92e95266e5a485b7660bf309645b18e56a5ddc 100755
--- a/bin/slubsipbuilder.pl
+++ b/bin/slubsipbuilder.pl
@@ -277,10 +277,10 @@ sub get_mods_from ($$) { # $mods = ($url, $ppn)
 
 sub main {
     # get date
-    my $export_to_archive_date = DateTime->now->iso8601();#
+    my $export_to_archive_date = DateTime->now->iso8601();
     my $file_date = $export_to_archive_date;
-    $file_date =~ s/T/_/g;
-    $file_date =~ s/:/-/g;
+    $file_date =~ s/T/_/g; # replace 'T' with '_'
+    $file_date =~ s/:/-/g; # replace ':' with '-'
     # create output dir
     if (! -d $output) {
         mkpath("$output") || confess("could not create SIP directory for '$output', $!");