diff --git a/5-network/09-resume-upload/article.md b/5-network/09-resume-upload/article.md
index f5c9a590..7eedc3fb 100644
--- a/5-network/09-resume-upload/article.md
+++ b/5-network/09-resume-upload/article.md
@@ -24,7 +24,7 @@ To resume upload, we need to know *exactly* the number of bytes received by the
 
 1. First, create a file id, to uniquely identify the file we're going to upload:
     ```js
-    let fileId = file.name + '-' + file.size + '-' + +file.lastModifiedDate;
+    let fileId = file.name + '-' + file.size + '-' + file.lastModified;
     ```
     That's needed for resume upload, to tell the server what we're resuming.
 
diff --git a/5-network/09-resume-upload/upload-resume.view/uploader.js b/5-network/09-resume-upload/upload-resume.view/uploader.js
index 2e53ce4a..10002039 100644
--- a/5-network/09-resume-upload/upload-resume.view/uploader.js
+++ b/5-network/09-resume-upload/upload-resume.view/uploader.js
@@ -6,7 +6,7 @@ class Uploader {
 
     // create fileId that uniquely identifies the file
     // we could also add user session identifier (if had one), to make it even more unique
-    this.fileId = file.name + '-' + file.size + '-' + +file.lastModifiedDate;
+    this.fileId = file.name + '-' + file.size + '-' + file.lastModified;
   }
 
   async getUploadedBytes() {