diff --git a/core/lib/Drupal/Core/Form/EventSubscriber/FormAjaxSubscriber.php b/core/lib/Drupal/Core/Form/EventSubscriber/FormAjaxSubscriber.php
index 054e262..ffbd8f3 100644
--- a/core/lib/Drupal/Core/Form/EventSubscriber/FormAjaxSubscriber.php
+++ b/core/lib/Drupal/Core/Form/EventSubscriber/FormAjaxSubscriber.php
@@ -79,12 +79,12 @@ public function onException(GetResponseForExceptionEvent $event) {
   protected function getFormAjaxException(\Exception $e) {
     $exception = NULL;
     while ($e) {
-      if (!$e instanceof FormAjaxException) {
-        $e = $e->getPrevious();
+      if ($e instanceof FormAjaxException) {
+        $exception = $e;
+        break;
       }
 
-      $exception = $e;
-      break;
+      $e = $e->getPrevious();
     }
     return $exception;
   }
diff --git a/core/tests/Drupal/Tests/Core/Form/EventSubscriber/FormAjaxSubscriberTest.php b/core/tests/Drupal/Tests/Core/Form/EventSubscriber/FormAjaxSubscriberTest.php
index bd645f6..eb01501 100644
--- a/core/tests/Drupal/Tests/Core/Form/EventSubscriber/FormAjaxSubscriberTest.php
+++ b/core/tests/Drupal/Tests/Core/Form/EventSubscriber/FormAjaxSubscriberTest.php
@@ -159,6 +159,20 @@ public function testOnExceptionNestedException() {
   }
 
   /**
+   * @covers ::getFormAjaxException
+   */
+  public function testOnExceptionNestedWrongException() {
+    $nested_exception = new \Exception();
+    $exception = new \Exception('', 0, $nested_exception);
+    $request = new Request();
+
+    $this->formAjaxResponseBuilder->expects($this->never())
+      ->method('buildResponse');
+
+    $this->assertResponseFromException($request, $exception, NULL);
+  }
+
+  /**
    * Asserts that the expected response is derived from the given exception.
    *
    * @param \Symfony\Component\HttpFoundation\Request $request