diff --git a/core/modules/language/lib/Drupal/language/Tests/LanguageUILanguageNegotiationTest.php b/core/modules/language/lib/Drupal/language/Tests/LanguageUILanguageNegotiationTest.php
index e614da2..a6c1dc7 100644
--- a/core/modules/language/lib/Drupal/language/Tests/LanguageUILanguageNegotiationTest.php
+++ b/core/modules/language/lib/Drupal/language/Tests/LanguageUILanguageNegotiationTest.php
@@ -462,11 +462,11 @@ function testLanguageDomain() {
     $this->assertTrue($italian_url == $correct_link, format_string('The url() function returns the right URL (@url) in accordance with the chosen language', array('@url' => $italian_url)));
 
     // Test HTTPS via options.
-    variable_set('https', TRUE);
+    $this->settingsSet('mixed_mode_sessions', TRUE);
     $italian_url = url('admin', array('https' => TRUE, 'language' => $languages['it'], 'script' => ''));
     $correct_link = 'https://' . $link;
     $this->assertTrue($italian_url == $correct_link, format_string('The url() function returns the right HTTPS URL (via options) (@url) in accordance with the chosen language', array('@url' => $italian_url)));
-    variable_set('https', FALSE);
+    $this->settingsSet('mixed_mode_sessions', FALSE);
 
     // Test HTTPS via current URL scheme.
     $temp_https = $is_https;
diff --git a/core/modules/system/lib/Drupal/system/Tests/Session/SessionHttpsTest.php b/core/modules/system/lib/Drupal/system/Tests/Session/SessionHttpsTest.php
index 0ab45a9..787b7d0 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Session/SessionHttpsTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Session/SessionHttpsTest.php
@@ -113,7 +113,13 @@ protected function testHttpsSession() {
     }
 
     // Enable secure pages.
-    variable_set('https', TRUE);
+    $this->settingsSet('mixed_mode_sessions', TRUE);
+    // Write that value also into the test settings.php file.
+    $settings['settings']['mixed_mode_sessions'] = (object) array(
+      'value' => TRUE,
+      'required' => TRUE,
+    );
+    $this->writeSettings($settings);
 
     $this->curlClose();
     // Start an anonymous session on the insecure site.