diff --git a/htdocs/user/class/user.class.php b/htdocs/user/class/user.class.php
index b6db00d2d16..488414f24c6 100644
--- a/htdocs/user/class/user.class.php
+++ b/htdocs/user/class/user.class.php
@@ -1124,7 +1124,7 @@ class User extends CommonObject
 		// Clean parameters
 
 		if (!empty($conf->global->MAIN_FIRST_TO_UPPER)) $this->lastname = ucwords($this->lastname);
-		if (!empty($conf->global->MAIN_ALL_TO_UPPER)) $this->lastname = strtoupper($this->lastname);
+		if (!empty($conf->global->MAIN_ALL_TO_UPPER)) $this->lastname = dol_strtoupper($this->lastname);
 		if (!empty($conf->global->MAIN_FIRST_TO_UPPER)) $this->firstname = ucwords($this->firstname);
 
 		$this->login = trim($this->login);
@@ -1469,7 +1469,7 @@ class User extends CommonObject
 		// Clean parameters
 
 		if (!empty($conf->global->MAIN_FIRST_TO_UPPER)) $this->lastname = ucwords($this->lastname);
-		if (!empty($conf->global->MAIN_ALL_TO_UPPER)) $this->lastname = strtoupper($this->lastname);
+		if (!empty($conf->global->MAIN_ALL_TO_UPPER)) $this->lastname = dol_strtoupper($this->lastname);
 		if (!empty($conf->global->MAIN_FIRST_TO_UPPER)) $this->firstname = ucwords($this->firstname);
 
 		$this->lastname     = trim($this->lastname);