diff --git a/htdocs/core/lib/functions.lib.php b/htdocs/core/lib/functions.lib.php
index 5d1a977d049..f27224c645f 100644
--- a/htdocs/core/lib/functions.lib.php
+++ b/htdocs/core/lib/functions.lib.php
@@ -616,7 +616,7 @@ if (! function_exists('dol_getprefix'))
     /**
      *  Return a prefix to use for this Dolibarr instance, for session/cookie names or email id.
      *  The prefix for session is unique in a web context only and is unique for instance and avoid conflict
-     *  between multi-instances, even when having two instances with one root dir or two instances in virtual servers.
+     *  between multi-instances, even when having two instances with same root dir or two instances in same virtual server.
      *  The prefix for email is unique if MAIL_PREFIX_FOR_EMAIL_ID is set to a value, otherwise value may be same than other instance.
      *
      *  @param  string  $mode                   '' (prefix for session name) or 'email' (prefix for email id)
@@ -634,16 +634,16 @@ if (! function_exists('dol_getprefix'))
 				if ($conf->global->MAIL_PREFIX_FOR_EMAIL_ID != 'SERVER_NAME') return $conf->global->MAIL_PREFIX_FOR_EMAIL_ID;
 				else if (isset($_SERVER["SERVER_NAME"])) return $_SERVER["SERVER_NAME"];
 			}
-			return dol_hash(DOL_DOCUMENT_ROOT.DOL_URL_ROOT);
+			return dol_hash(DOL_DOCUMENT_ROOT.DOL_URL_ROOT, '3');
 		}
 
 		if (isset($_SERVER["SERVER_NAME"]) && isset($_SERVER["DOCUMENT_ROOT"]))
 		{
-			return dol_hash($_SERVER["SERVER_NAME"].$_SERVER["DOCUMENT_ROOT"].DOL_DOCUMENT_ROOT.DOL_URL_ROOT);
-			// Use this for a "readable" cookie name
+			return dol_hash($_SERVER["SERVER_NAME"].$_SERVER["DOCUMENT_ROOT"].DOL_DOCUMENT_ROOT.DOL_URL_ROOT, '3');
+			// Use this for a "readable" key
 			//return dol_sanitizeFileName($_SERVER["SERVER_NAME"].$_SERVER["DOCUMENT_ROOT"].DOL_DOCUMENT_ROOT.DOL_URL_ROOT);
 		}
-		return dol_hash(DOL_DOCUMENT_ROOT.DOL_URL_ROOT);
+		return dol_hash(DOL_DOCUMENT_ROOT.DOL_URL_ROOT, '3');
 	}
 }