diff --git a/php/model/LocalArticleManager.php b/php/model/LocalArticleManager.php
index 8836b72..2789da9 100644
--- a/php/model/LocalArticleManager.php
+++ b/php/model/LocalArticleManager.php
@@ -45,7 +45,7 @@ class LocalArticleManager implements ArticleManagerDAO {
         );
     }
 
-    public function addArticle($title, $content, $author, $category, $tags)
+    public function addArticle(string $title, string $content, string $author, string $category, string $tags)
     {
         $articles = $this->getAllArticles();