diff --git a/core/tests/Drupal/FunctionalTests/BrowserTestBaseTest.php b/core/tests/Drupal/FunctionalTests/BrowserTestBaseTest.php
index 882e6edcd7..0ed9a3b248 100644
--- a/core/tests/Drupal/FunctionalTests/BrowserTestBaseTest.php
+++ b/core/tests/Drupal/FunctionalTests/BrowserTestBaseTest.php
@@ -633,4 +633,11 @@ public function testCheckForMetaRefresh() {
     $this->assertSession()->pageTextContains('Test page text.');
   }
 
+  public function testGetDefaultDriveInstance() {
+    putenv('MINK_DRIVER_ARGS=' . json_encode([NULL, ['key1' => ['key2' => ['key3' => 3, 'key3.1' => 3.1]]]]));
+    $this->getDefaultDriverInstance();
+    $this->assertEquals([NULL, ['key1' => ['key2' => ['key3' => 3, 'key3.1' => 3.1]]]], $this->minkDefaultDriverArgs);
+  }
+
 }
+
diff --git a/core/tests/Drupal/Tests/BrowserTestBase.php b/core/tests/Drupal/Tests/BrowserTestBase.php
index e7c79f380a..6ac72f30c3 100644
--- a/core/tests/Drupal/Tests/BrowserTestBase.php
+++ b/core/tests/Drupal/Tests/BrowserTestBase.php
@@ -342,7 +342,7 @@ protected function initMink() {
   protected function getDefaultDriverInstance() {
     // Get default driver params from environment if availables.
     if ($arg_json = getenv('MINK_DRIVER_ARGS')) {
-      $this->minkDefaultDriverArgs = json_decode($arg_json);
+      $this->minkDefaultDriverArgs = json_decode($arg_json, TRUE);
     }
 
     // Get and check default driver class from environment if availables.