diff --git a/htdocs/filefunc.inc.php b/htdocs/filefunc.inc.php
index dfaa4f78571..3be6cadc9ce 100644
--- a/htdocs/filefunc.inc.php
+++ b/htdocs/filefunc.inc.php
@@ -152,26 +152,29 @@ if (! empty($dolibarr_main_document_root_alt))
 // Define DOL_MAIN_URL_ROOT and DOL_URL_ROOT
 $tmp='';
 $found=0;
-$real_dolibarr_main_document_root=str_replace('\\','/',realpath($dolibarr_main_document_root));	// A) Ex: C:/xxx/dolibarr/htdocs
-$pathroot=$_SERVER["DOCUMENT_ROOT"];															// B) Ex: C:/Program Files/wamp/www/
-$paths=explode('/',str_replace('\\','/',$_SERVER["SCRIPT_NAME"]));								// C) Ex: /dolibarr/htdocs/admin/system/phpinfo.php
+$real_dolibarr_main_document_root=str_replace('\\','/',realpath($dolibarr_main_document_root));	// A) Value found into config file, to say where are store htdocs files. Ex: C:/xxx/dolibarr, C:/xxx/dolibarr/htdocs
+$pathroot=$_SERVER["DOCUMENT_ROOT"];															// B) Value reported by web server setup, to say where is root of web server instance. Ex: C:/xxx/dolibarr, C:/xxx/dolibarr/htdocs
+$paths=explode('/',str_replace('\\','/',$_SERVER["SCRIPT_NAME"]));								// C) Value reported by web server, to say full path on filesystem of a file. Ex: /dolibarr/htdocs/admin/system/phpinfo.php
+// Try to detect if $_SERVER["DOCUMENT_ROOT"]+start of $_SERVER["SCRIPT_NAME"] is $dolibarr_main_document_root. If yes, relative url to add before dol files is this start part.
 $concatpath='';
 foreach($paths as $tmppath)	// We check to find (B+start of C)=A
 {
-    if ($tmppath) $concatpath.='/'.$tmppath;
+    if (empty($tmppath)) continue;
+    $concatpath.='/'.$tmppath;
+    //if ($tmppath) $concatpath.='/'.$tmppath;
     //print $_SERVER["SCRIPT_NAME"].'-'.$pathroot.'-'.$concatpath.'-'.$real_dolibarr_main_document_root.'-'.realpath($pathroot.$concatpath).'<br>';
     if ($real_dolibarr_main_document_root == @realpath($pathroot.$concatpath))    // @ avoid warning when safe_mode is on.
     {
-        $tmp3=$concatpath;
-        //print "Found relative url = ".$tmp3;
+        //print "Found relative url = ".$concatpath;
+    	$tmp3=$concatpath;
         $found=1;
         break;
     }
     //else print "Not found yet for concatpath=".$concatpath."<br>\n";
 }
-if (! $found) $tmp=$dolibarr_main_url_root; // If autodetect fails (Ie: when using apache alias that point outside default DOCUMENT_ROOT.
+if (! $found) $tmp=$dolibarr_main_url_root; // If autodetect fails (Ie: when using apache alias that point outside default DOCUMENT_ROOT).
 else $tmp='http'.(((empty($_SERVER["HTTPS"]) || $_SERVER["HTTPS"] != 'on') && (empty($_SERVER["SERVER_PORT"])||$_SERVER["SERVER_PORT"]!=443))?'':'s').'://'.$_SERVER["SERVER_NAME"].((empty($_SERVER["SERVER_PORT"])||$_SERVER["SERVER_PORT"]==80||$_SERVER["SERVER_PORT"]==443)?'':':'.$_SERVER["SERVER_PORT"]).($tmp3?(preg_match('/^\//',$tmp3)?'':'/').$tmp3:'');
-//print "tmp1=".$tmp1." tmp2=".$tmp2." tmp3=".$tmp3." tmp=".$tmp;
+//print "tmp1=".$tmp1." tmp2=".$tmp2." tmp3=".$tmp3." tmp=".$tmp."\n";
 if (! empty($dolibarr_main_force_https)) $tmp=preg_replace('/^http:/i','https:',$tmp);
 define('DOL_MAIN_URL_ROOT', $tmp);											// URL absolute root (https://sss/dolibarr, ...)
 $uri=preg_replace('/^http(s?):\/\//i','',constant('DOL_MAIN_URL_ROOT'));	// $uri contains url without http*