diff --git a/php/model/Comment.php b/php/model/Comment.php
index 47595f8..b92543b 100644
--- a/php/model/Comment.php
+++ b/php/model/Comment.php
@@ -80,7 +80,7 @@ class Comment
      */
     public function isReply(): bool
     {
-        return $this->parentCommentId !== null;
+        return $this->parentCommentId !== null && $this->parentCommentId !== 0;
     }
 
     /**
diff --git a/php/model/DatabaseCommentManager.php b/php/model/DatabaseCommentManager.php
index 8cd66cf..3bba78c 100644
--- a/php/model/DatabaseCommentManager.php
+++ b/php/model/DatabaseCommentManager.php
@@ -113,6 +113,10 @@ class DatabaseCommentManager implements CommentManagerDAO
         try {
             $db = $this->getConnection();
 
+            if ($parentCommentId === "" || $parentCommentId === 0 || $parentCommentId === "0") {
+                $parentCommentId = null;
+            }
+
             $sql = "
                 INSERT INTO comments (
                     article_id,
@@ -173,12 +177,21 @@ class DatabaseCommentManager implements CommentManagerDAO
             $comments = [];
 
             while ($row = $command->fetch(PDO::FETCH_ASSOC)) {
+                $parentCommentId = null;
+
+                if (
+                    isset($row["parent_comment_id"])
+                    && $row["parent_comment_id"] !== null
+                    && $row["parent_comment_id"] !== ""
+                    && intval($row["parent_comment_id"]) !== 0
+                ) {
+                    $parentCommentId = intval($row["parent_comment_id"]);
+                }
+
                 $comments[] = new Comment(
                     intval($row["id"]),
                     intval($row["article_id"]),
-                    isset($row["parent_comment_id"]) && $row["parent_comment_id"] !== null
-                        ? intval($row["parent_comment_id"])
-                        : null,
+                    $parentCommentId,
                     $row["author"],
                     $row["content"],
                     $row["created"]