diff --git a/core/lib/Drupal/Core/Config/ConfigBase.php b/core/lib/Drupal/Core/Config/ConfigBase.php
index 2999b76..b0db1b6 100644
--- a/core/lib/Drupal/Core/Config/ConfigBase.php
+++ b/core/lib/Drupal/Core/Config/ConfigBase.php
@@ -176,6 +176,8 @@ public function setData(array $data) {
    * @param array $data
    *   Configuration array structure.
    *
+   * @return null
+   *
    * @throws \Exception
    *   If any key in $data in any depth contains a dot.
    */
@@ -200,10 +202,16 @@ protected function validateKeys(array $data) {
    *
    * @return $this
    *   The configuration object.
+   *
+   * @throws \Exception
+   *   If $value is an array and any of its keys in any depth contains a dot.
    */
   public function set($key, $value) {
     // The dot/period is a reserved character; it may appear between keys, but
     // not within keys.
+    if (is_array($value)) {
+      $this->validateKeys($value);
+    }
     $parts = explode('.', $key);
     if (count($parts) == 1) {
       $this->data[$key] = $value;