diff --git a/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
index 0856611..615c85e 100644
--- a/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
@@ -804,6 +804,13 @@ abstract class WebTestBase extends TestBase {
 
     if (!isset($this->curlHandle)) {
       $this->curlHandle = curl_init();
+
+      // Some versions/configurations of cURL break on a NULL cookie jar, so
+      // supply a real file.
+      if (!isset($this->cookieFile)) {
+        $this->cookieFile = $this->public_files_directory . '/cookie.jar';
+      }
+
       $curl_options = array(
         CURLOPT_COOKIEJAR => $this->cookieFile,
         CURLOPT_URL => $base_url,
@@ -818,7 +825,12 @@ abstract class WebTestBase extends TestBase {
         $curl_options[CURLOPT_HTTPAUTH] = $this->httpauth_method;
         $curl_options[CURLOPT_USERPWD] = $this->httpauth_credentials;
       }
-      curl_setopt_array($this->curlHandle, $this->additionalCurlOptions + $curl_options);
+      // curl_setopt_array() returns FALSE if any of the specified options
+      // cannot be set, and stops processing any further options.
+      $result = curl_setopt_array($this->curlHandle, $this->additionalCurlOptions + $curl_options);
+      if (!$result) {
+        throw new \UnexpectedValueException('One or more cURL options could not be set.');
+      }
 
       // By default, the child session name should be the same as the parent.
       $this->session_name = session_name();