diff --git a/server/router/versions/index.js b/server/router/versions/index.js
index 4fb119f..28ccdb7 100644
--- a/server/router/versions/index.js
+++ b/server/router/versions/index.js
@@ -384,7 +384,7 @@ module.exports = function (options) {
                             const chapter = await saveFile(
                                 file,
                                 request.user.id,
-                                chapterIndex+index,
+                                Number(chapterIndex)+Number(index),
                                 artifactVersion
                             )
                         }