diff -u b/core/includes/batch.inc b/core/includes/batch.inc
--- b/core/includes/batch.inc
+++ b/core/includes/batch.inc
@@ -293,7 +293,7 @@
         // \Drupal\simpletest\WebTestBase::$memoryUsageTrigger to ensure that
         // Drupal works under that limit.
         // @see \Drupal\simpletest\WebTestBase::curlHeaderCallback
-        $maximum_memory = '64M';
+        $maximum_memory = '32M';
       }
       else {
         $maximum_memory = ini_get('memory_limit');
diff -u b/core/modules/simpletest/src/WebTestBase.php b/core/modules/simpletest/src/WebTestBase.php
--- b/core/modules/simpletest/src/WebTestBase.php
+++ b/core/modules/simpletest/src/WebTestBase.php
@@ -76,7 +76,7 @@
    *
    * @var string|FALSE
    */
-  protected $memoryUsageTrigger = '64M';
+  protected $memoryUsageTrigger = '32M';
 
   /**
    * The handle of the current cURL connection.