Index: Bugzilla/Template.pm
===================================================================
--- Bugzilla/Template.pm
+++ Bugzilla/Template.pm
@@ -284,7 +284,8 @@
 
         $link_text =~ s/ \[details\]$//;
         $link_text =~ s/ \[diff\]$//;
-        my $linkval = "attachment.cgi?id=$attachid";
+        state $urlbase = Bugzilla->localconfig->{urlbase};
+        my $linkval = "${urlbase}attachment.cgi?id=$attachid";
 
         # If the attachment is a patch and patch_viewer feature is
         # enabled, add link to the diff.