diff --git a/src/Plugin.php b/src/Plugin.php
index d99b3b8dcb10c5a039630397c25c1d7ae39b6927..870c9c75a657e45a42e0f2b2dd4f5ce39669d22a 100644
--- a/src/Plugin.php
+++ b/src/Plugin.php
@@ -83,7 +83,7 @@ class Plugin implements PluginInterface {
             $extra[$item][$path] = ['type:drupal-' . $type];
           }
         }
-        $extra[$item] += $this->readJson($item, $extra[$key], $io);
+        $extra[$item] = array_merge($extra[$item], $this->readJson($item, $extra[$key], $io));
         $changed = TRUE;
       }
     }