diff --git a/tests/sshserver.pl b/tests/sshserver.pl
index 6781554f66..2f9cef0fcb 100755
--- a/tests/sshserver.pl
+++ b/tests/sshserver.pl
@@ -422,6 +422,7 @@ if((! -e pp($hstprvkeyf)) || (! -s pp($hstprvkeyf)) ||
     system "chmod 600 " . pp($hstprvkeyf);
     system "chmod 600 " . pp($cliprvkeyf);
     if($^O eq 'cygwin' || $^O eq 'msys') {
+      # https://cygwin.com/cygwin-ug-net/setfacl.html
       system "setfacl --remove-all "                   . pp($hstprvkeyf);
       system "setfacl --modify u:" . $username . ":r " . pp($hstprvkeyf);
     }