diff --git a/classes/auth.php b/classes/auth.php
index 5b0f4ce3c..a6294014d 100644
--- a/classes/auth.php
+++ b/classes/auth.php
@@ -642,7 +642,7 @@ public function saml_login_complete($attributes) {
             $accentsensitive = true;
             if ($this->config->tolower == saml2_settings::OPTION_TOLOWER_LOWER_CASE) {
                 $this->log(__FUNCTION__ . " to lowercase for $uid");
-                $uid = strtolower($uid);
+                $uid = \core_text::strtolower($uid);
             }
             if ($this->config->tolower == saml2_settings::OPTION_TOLOWER_CASE_INSENSITIVE) {
                 $this->log(__FUNCTION__ . " case insensitive compare for $uid");
@@ -696,7 +696,7 @@ public function saml_login_complete($attributes) {
                 $this->update_user_record_from_attribute_map($user, $attributes, true);
                 if (empty($user->username)) {
                     // Just in case username field not set, use uid.
-                    $user->username = strtolower($uid);
+                    $user->username = \core_text::strtolower($uid);
                 }
                 // Set the auth to saml2 if it's not set from the attributes.
                 if (empty($user->auth)) {
@@ -979,7 +979,7 @@ public function update_user_record_from_attribute_map(&$user, $attributes, $newu
                                     }
                                 }
                                 if ($field == 'username') {
-                                    $user->$field = strtolower($attributes[$attr][0]);
+                                    $user->$field = \core_text::strtolower($attributes[$attr][0]);
                                 } else {
                                     // Custom profile fields have the prefix profile_field_ and will be saved as profile field data.
                                     $delimiter = $mapconfig->fielddelimiter;
@@ -1047,7 +1047,7 @@ public function get_email_from_attributes(array $attributes) {
      */
     private function get_username_from_attributes(array $attributes) {
         if (!empty($this->config->field_map_username) && !empty($attributes[$this->config->field_map_username])) {
-            return strtolower($attributes[$this->config->field_map_username][0]);
+            return \core_text::strtolower($attributes[$this->config->field_map_username][0]);
         }
 
         return false;
diff --git a/tests/behat/behat_auth_saml2.php b/tests/behat/behat_auth_saml2.php
index c7536bd62..4deab49f8 100644
--- a/tests/behat/behat_auth_saml2.php
+++ b/tests/behat/behat_auth_saml2.php
@@ -212,7 +212,7 @@ public function the_saml_setting_is_set_to_auth_saml($setting, $value) {
             $setting = 'flagmessage';
         }
 
-        $lowervalue = strtolower($value);
+        $lowervalue = core_text::strtolower($value);
         $value = array_key_exists($lowervalue, $map) ? $map[$lowervalue] : $value;
         set_config($setting, $value, 'auth_saml2');
     }