diff --git a/library/Icinga/Authentication/User/ExternalBackend.php b/library/Icinga/Authentication/User/ExternalBackend.php
index 62b1ea40e..30e816089 100644
--- a/library/Icinga/Authentication/User/ExternalBackend.php
+++ b/library/Icinga/Authentication/User/ExternalBackend.php
@@ -58,8 +58,8 @@ class ExternalBackend implements UserBackendInterface
      */
     public function authenticate(User $user, $password = null)
     {
-        if (isset($_SERVER['REMOTE_USER'])) {
-            $username = $_SERVER['REMOTE_USER'];
+        $username = getenv('REMOTE_USER');
+        if ($username !== false) {
             $user->setExternalUserInformation($username, 'REMOTE_USER');
 
             if ($this->stripUsernameRegexp) {
diff --git a/modules/setup/application/forms/AdminAccountPage.php b/modules/setup/application/forms/AdminAccountPage.php
index c0d5cff6f..94b83b897 100644
--- a/modules/setup/application/forms/AdminAccountPage.php
+++ b/modules/setup/application/forms/AdminAccountPage.php
@@ -269,11 +269,11 @@ class AdminAccountPage extends Form
      */
     protected function getUsername()
     {
-        if (false === isset($_SERVER['REMOTE_USER'])) {
+        $name = getenv('REMOTE_USER');
+        if ($name === false) {
             return '';
         }
 
-        $name = $_SERVER['REMOTE_USER'];
         if (isset($this->backendConfig['strip_username_regexp']) && $this->backendConfig['strip_username_regexp']) {
             // No need to silence or log anything here because the pattern has
             // already been successfully compiled during backend configuration
diff --git a/modules/setup/application/forms/AuthenticationPage.php b/modules/setup/application/forms/AuthenticationPage.php
index 370e4bb95..dada8ac84 100644
--- a/modules/setup/application/forms/AuthenticationPage.php
+++ b/modules/setup/application/forms/AuthenticationPage.php
@@ -30,7 +30,7 @@ class AuthenticationPage extends Form
      */
     public function createElements(array $formData)
     {
-        if (isset($formData['type']) && $formData['type'] === 'external' && !isset($_SERVER['REMOTE_USER'])) {
+        if (isset($formData['type']) && $formData['type'] === 'external' && getenv('REMOTE_USER') === false) {
             $this->info(
                 $this->translate(
                     'You\'re currently not authenticated using any of the web server\'s authentication '