diff --git a/htdocs/conf/conf.php.example b/htdocs/conf/conf.php.example
index a23c2f9cfbe..589cd212ef5 100644
--- a/htdocs/conf/conf.php.example
+++ b/htdocs/conf/conf.php.example
@@ -37,18 +37,17 @@ $dolibarr_main_document_root='';
 
 
 // dolibarr_main_url_root_alt
-// This parameter defines the alternative URL of your Dolibarr.
-// It must link to some other secondary htdocs directories, separated by a coma.
+// This parameter defines the relative sub URLs of alternative Dolibarr root directories.
+// It can be links to some other secondary htdocs directories, separated by a coma.
 // Examples:
-// $dolibarr_main_url_root_alt='http://localhost/extensions';
-// $dolibarr_main_url_root_alt='http://mydolibarrvirtualhost/extensions1,http://mydolibarrvirtualhost/extensions2';
+// $dolibarr_main_url_root_alt='/extensions';
+// $dolibarr_main_url_root_alt='/extensions1,/extensions2';
 //
 $dolibarr_main_url_root_alt='';
 
 
 // dolibarr_main_document_root_alt
-// This parameter contains absolute alternative file system directory of Dolibarr
-// It must link to url to other secondary htdocs directories, separated by a coma.
+// This parameter contains absolute alternative root file system directories of Dolibarr
 // Examples:
 // $dolibarr_main_document_root_alt='/var/www/dolibarr/htdocs/extensions';
 // $dolibarr_main_document_root_alt='C:/My web sites/dolibarr/htdocs/extensions1,C:/My web sites/dolibarr/htdocs/extensions2';
diff --git a/htdocs/filefunc.inc.php b/htdocs/filefunc.inc.php
index 483b71f3e07..7ff53d7cac6 100755
--- a/htdocs/filefunc.inc.php
+++ b/htdocs/filefunc.inc.php
@@ -175,22 +175,6 @@ $suburi = strstr($uri, '/');												// $suburi contains url without domain:p
 if ($suburi == '/') $suburi = '';											// If $suburi is /, it is now ''
 define('DOL_URL_ROOT', $suburi);											// URL relative root ('', '/dolibarr', ...)
 
-/*
-// Define DOL_MAIN_URL_ROOT_ALT and DOL_URL_ROOT_ALT (deprecated)
-if (! empty($dolibarr_main_url_root_alt))
-{
-    $altpart=str_replace($dolibarr_main_url_root,'',$dolibarr_main_url_root_alt);
-    if (! preg_match('/^\//',$altpart) && ! empty($altpart)) { $tmp_alt=$dolibarr_main_url_root_alt; }	// Manage case url=http://localhost/aaa and url_alt=http://localhost/aaabbb
-    else $tmp_alt=$tmp.((preg_match('/\/$/',$tmp)||preg_match('/^\//',$altpart))?'':'/').$altpart;
-	//$tmp_alt=$dolibarr_main_url_root_alt;
-    define('DOL_MAIN_URL_ROOT_ALT', $tmp_alt);           							// URL absolute root (https://sss/dolibarr/custom, ...)
-	$uri=preg_replace('/^http(s?):\/\//i','',constant('DOL_MAIN_URL_ROOT_ALT'));    // $uri contains url without http*
-	$suburi = strstr($uri, '/');        											// $suburi contains url without domain:port
-	if ($suburi == '/') $suburi = '';   											// If $suburi is /, it is now ''
-	define('DOL_URL_ROOT_ALT', $suburi);    										// URL relative root ('', '/dolibarr/custom', ...)
-}
-*/
-
 //print DOL_URL_ROOT;
 
 // Define prefix MAIN_DB_PREFIX
diff --git a/htdocs/master.inc.php b/htdocs/master.inc.php
index 3505a3b13fa..9e1c5ad2e14 100644
--- a/htdocs/master.inc.php
+++ b/htdocs/master.inc.php
@@ -74,7 +74,20 @@ if (! empty($dolibarr_main_document_root_alt))
 	foreach($values as $value) $conf->file->dol_document_root['alt'.($i++)]=(string) $value;
 	$values=preg_split('/[;,]/',$dolibarr_main_url_root_alt);
 	$i=0;
-	foreach($values as $value)	$conf->file->dol_url_root['alt'.($i++)]=(string) $value;
+	foreach($values as $value)
+	{
+		if (preg_match('/^http(s)?:/',$value))
+		{
+			print 'Error: values for <b>$dolibarr_main_url_root_alt</b> into <b>conf.php</b> file must contains relative path to alternative URLs.<br>'."\n";
+			print "Found: \"".$value."\"<br>\n";
+			print "Should found something like following examples:<br>\n";
+			print "\"/extensions\"<br>\n";
+			print "\"/extensions1,/extensions2,...\"<br>\n";
+			print "\"/custom\"<br>\n";
+			exit;
+		}
+		$conf->file->dol_url_root['alt'.($i++)]=(string) $value;
+	}
 }
 
 // Set properties specific to multicompany