diff --git a/core/tests/Drupal/FunctionalJavascriptTests/JavascriptTestBase.php b/core/tests/Drupal/FunctionalJavascriptTests/JavascriptTestBase.php
index ae3ed62..c190ee2 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/JavascriptTestBase.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/JavascriptTestBase.php
@@ -39,7 +39,12 @@ protected function initMink() {
   protected function tearDown() {
     // Wait for all requests to finish. It is possible that an AJAX request is
     // still on-going.
-    $this->getSession()->wait(5000, '(typeof(jQuery)=="undefined" || (0 === jQuery.active && 0 === jQuery(\':animated\').length))');
+    $result = $this->getSession()->wait(5000, '(typeof(jQuery)=="undefined" || (0 === jQuery.active && 0 === jQuery(\':animated\').length))');
+    if (!$result) {
+      // Throw an exception to ensure errors are not obfuscated by missing
+      // session table errors.
+      throw new \RuntimeException('Unfinished AJAX requests whilst tearing down a test');
+    }
     parent::tearDown();
   }