diff --git a/core/lib/Drupal/Core/Config/TypedConfigManager.php b/core/lib/Drupal/Core/Config/TypedConfigManager.php
index 1181953..0871b9e 100644
--- a/core/lib/Drupal/Core/Config/TypedConfigManager.php
+++ b/core/lib/Drupal/Core/Config/TypedConfigManager.php
@@ -171,9 +171,10 @@ protected function getDefinitionWithReplacements($base_plugin_id, array $replace
       // Replace dynamic portions of the definition type.
       if (!empty($replacements) && strpos($definition['type'], ']')) {
         $sub_type = $this->determineType($this->replaceName($definition['type'], $replacements), $definitions);
+        $sub_merge = $this->getDefinition($definitions[$sub_type]['type'], $exception_on_invalid);
         // Merge the newly determined subtype definition with the original
         // definition.
-        $definition = NestedArray::mergeDeepArray([$definitions[$sub_type], $definition], TRUE);
+        $definition = NestedArray::mergeDeepArray([$sub_merge, $definition], TRUE);
         $type = "$type||$sub_type";
       }
       // Unset type so we try the merge only once per type.