diff --git a/core/lib/Drupal/Core/Config/Config.php b/core/lib/Drupal/Core/Config/Config.php
index 8c9747a..ff99c27 100644
--- a/core/lib/Drupal/Core/Config/Config.php
+++ b/core/lib/Drupal/Core/Config/Config.php
@@ -217,14 +217,8 @@ public function save() {
       }
     }
     else {
-      // Minimal validation. Should not try to serialize resources or non-arrays.
       foreach ($this->data as $key => $value) {
-        if (is_resource($value) || (!is_scalar($value) && !is_array($value))) {
-          throw new UnsupportedDataTypeConfigException(String::format('Invalid data type for config element @name:@key', array(
-            '@name' => $this->getName(),
-            '@key' => $key,
-          )));
-        }
+        $this->validateValue($key, $value);
       }
     }
 
diff --git a/core/lib/Drupal/Core/Config/StorableConfigBase.php b/core/lib/Drupal/Core/Config/StorableConfigBase.php
index 238cd8b..18c0f07 100644
--- a/core/lib/Drupal/Core/Config/StorableConfigBase.php
+++ b/core/lib/Drupal/Core/Config/StorableConfigBase.php
@@ -132,6 +132,27 @@ protected function getSchemaWrapper() {
   }
 
   /**
+   * Validate the values are allowed data types.
+   *
+   * @throws UnsupportedDataTypeConfigException
+   *   If there is any invalid value.
+   */
+  protected function validateValue($key, $value) {
+    // Minimal validation. Should not try to serialize resources or non-arrays.
+    if (is_array($value)) {
+      foreach ($value as $nested_value_key => $nested_value) {
+        $this->validateValue($key . '.' . $nested_value_key, $nested_value);
+      }
+    }
+    elseif ($value !== NULL && !is_scalar($value)) {
+      throw new UnsupportedDataTypeConfigException(String::format('Invalid data type for config element @name:@key', array(
+        '@name' => $this->getName(),
+        '@key' => $key,
+      )));
+    }
+  }
+
+  /**
    * Casts the value to correct data type using the configuration schema.
    *
    * @param string $key
@@ -149,7 +170,7 @@ protected function castValue($key, $value) {
     if ($value === NULL) {
       $value = NULL;
     }
-    elseif (is_scalar($value) && !is_resource($value)) {
+    elseif (is_scalar($value)) {
       try {
         $element = $this->getSchemaWrapper()->get($key);
         if ($element instanceof PrimitiveInterface) {