diff --git a/core/tests/Drupal/FunctionalJavascriptTests/JavascriptTestBase.php b/core/tests/Drupal/FunctionalJavascriptTests/JavascriptTestBase.php
index 6a8f1f58bf31b0526f4a27fde14c7ffc603dd4f2..eecafb08acedcb98cb9f5f1ca63d30abfcf211b6 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/JavascriptTestBase.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/JavascriptTestBase.php
@@ -47,16 +47,18 @@ protected function initMink() {
    * {@inheritdoc}
    */
   protected function tearDown() {
-    // Wait for all requests to finish. It is possible that an AJAX request is
-    // still on-going.
-    $result = $this->getSession()->wait(5000, '(typeof(jQuery)=="undefined" || (0 === jQuery.active && 0 === jQuery(\':animated\').length))');
-    if (!$result) {
-      // If the wait is unsuccessful, there may still be an AJAX request in
-      // progress. If we tear down now, then this AJAX request may fail with
-      // missing database tables, because tear down will have removed them. Rather
-      // than allow it to fail, throw an explicit exception now explaining what
-      // the problem is.
-      throw new \RuntimeException('Unfinished AJAX requests whilst tearing down a test');
+    if ($this->mink) {
+      // Wait for all requests to finish. It is possible that an AJAX request is
+      // still on-going.
+      $result = $this->getSession()->wait(5000, '(typeof(jQuery)=="undefined" || (0 === jQuery.active && 0 === jQuery(\':animated\').length))');
+      if (!$result) {
+        // If the wait is unsuccessful, there may still be an AJAX request in
+        // progress. If we tear down now, then this AJAX request may fail with
+        // missing database tables, because tear down will have removed them.
+        // Rather than allow it to fail, throw an explicit exception now
+        // explaining what the problem is.
+        throw new \RuntimeException('Unfinished AJAX requests while tearing down a test');
+      }
     }
     parent::tearDown();
   }
diff --git a/core/tests/Drupal/Tests/BrowserTestBase.php b/core/tests/Drupal/Tests/BrowserTestBase.php
index d4b31d79be21fb897ba1693790726840b1b3b549..1ab59b6cf5f332057a58964fc822b8cae170d1ad 100644
--- a/core/tests/Drupal/Tests/BrowserTestBase.php
+++ b/core/tests/Drupal/Tests/BrowserTestBase.php
@@ -263,7 +263,9 @@ abstract class BrowserTestBase extends \PHPUnit_Framework_TestCase {
   /**
    * Mink session manager.
    *
-   * @var \Behat\Mink\Mink
+   * This will not be initialized if there was an error during the test setup.
+   *
+   * @var \Behat\Mink\Mink|null
    */
   protected $mink;