gistfile1.txt

diff --git a/core/lib/Drupal/Core/Config/TypedConfigManager.php b/core/lib/Drupal/Core/Config/TypedConfigManager.php
index 6ccf8fd..6415e6b 100644
--- a/core/lib/Drupal/Core/Config/TypedConfigManager.php
+++ b/core/lib/Drupal/Core/Config/TypedConfigManager.php
@@ -153,15 +153,15 @@ public function getDefinition($base_plugin_id, $exception_on_invalid = TRUE, $va
       // If the sub type has a bracket then lets look that up as well.
       if (isset($value) && strpos($definition['type'], ']')) {
         $sub_type = $this->replaceName($definition['type'], $value);
-        $merge = $definitions[$sub_type];
-        $definition = NestedArray::mergeDeepArray(array($merge, $definition), TRUE);
+        $sub_type_merge = $this->getDefinition($sub_type);
+        $definition = NestedArray::mergeDeepArray(array($sub_type_merge, $definition), TRUE);
       }