diff --git a/htdocs/main.inc.php b/htdocs/main.inc.php
index 0bfda0b15eb..e382d0200fb 100644
--- a/htdocs/main.inc.php
+++ b/htdocs/main.inc.php
@@ -871,13 +871,13 @@ function top_htmlhead($head, $title='', $disablejs=0, $disablehead=0, $arrayofjs
         // CSS forced by modules (relative url starting with /)
         if (is_array($conf->css_modules))
         {
-            foreach($conf->css_modules as $cssfile)
+            foreach($conf->css_modules as $key => $cssfile)
             {
                 // cssfile is an absolute path
                 print '<link rel="stylesheet" type="text/css" title="default" href="'.dol_buildpath($cssfile,1);
                 // We add params only if page is not static, because some web server setup does not return content type text/css if url has parameters, so browser cache is not used.
                 if (!preg_match('/\.css$/i',$cssfile)) print $themeparam;
-                print '">'."\n";
+                print '"><!-- Added by module '.$key. '-->'."\n";
             }
         }
         // CSS forced by page in top_htmlhead call (relative url starting with /)
@@ -888,7 +888,7 @@ function top_htmlhead($head, $title='', $disablejs=0, $disablehead=0, $arrayofjs
                 print '<link rel="stylesheet" type="text/css" title="default" href="'.dol_buildpath($cssfile,1);
                 // We add params only if page is not static, because some web server setup does not return content type text/css if url has parameters and browser cache is not used.
                 if (!preg_match('/\.css$/i',$cssfile)) print $themeparam;
-                print '">'."\n";
+                print '"><!-- Added by page -->'."\n";
             }
         }