diff --git a/src/Drupal/Driver/Cores/Drupal8.php b/src/Drupal/Driver/Cores/Drupal8.php
index 13234163..119bac2d 100644
--- a/src/Drupal/Driver/Cores/Drupal8.php
+++ b/src/Drupal/Driver/Cores/Drupal8.php
@@ -520,8 +520,8 @@ public function startCollectingMail() {
     $config = \Drupal::configFactory()->getEditable('system.mail');
     $data = $config->getRawData();
 
-    // Save the original values for restoration after.
-    $this->originalConfiguration['system.mail'] = $data;
+    // Save the values for restoration after.
+    $this->storeOriginalConfiguration('system.mail', $data);
 
     // @todo Use a collector that supports html after D#2223967 lands.
     $data['interface'] = ['default' => 'test_mail_collector'];
@@ -583,7 +583,7 @@ protected function startCollectingMailSystemMail() {
       $data = $config->getRawData();
 
       // Track original data for restoration.
-      $this->originalConfiguration['mailsystem.settings'] = $data;
+      $this->storeOriginalConfiguration('mailsystem.settings', $data);
 
       // Convert all of the 'senders' to the test collector.
       $data = $this->findMailSystemSenders($data);
@@ -619,4 +619,20 @@ protected function stopCollectingMailSystemMail() {
     }
   }
 
+  /**
+   * Store the original value for a piece of configuration.
+   *
+   * If an original value has previously been stored, it is not updated.
+   *
+   * @param string $name
+   *   The name of the configuration.
+   * @param mixed $value
+   *   The original value of the configuration.
+   */
+  protected function storeOriginalConfiguration($name, $value) {
+    if (!isset($this->originalConfiguration[$name])) {
+      $this->originalConfiguration[$name] = $value;
+    }
+  }
+
 }