diff --git a/src/js/Connection.js b/src/js/Connection.js
index 245d663..c486bed 100644
--- a/src/js/Connection.js
+++ b/src/js/Connection.js
@@ -644,7 +644,7 @@ class Connection {
 
         // update file transfer progress
         fileTransfer.status = FileTransferrer.STATUS_SENDING;
-        fileTransfer.progress = Math.min(100, Math.ceil(requestFileChunk.offset + requestFileChunk.length / fileTransfer.filesize * 100));
+        fileTransfer.progress = Math.min(100, Math.ceil((requestFileChunk.offset + requestFileChunk.length) / fileTransfer.filesize * 100));
 
         // send file part
         await FileTransferrer.sendFileChunk(fileTransfer, requestFileChunk.offset, requestFileChunk.length);
diff --git a/src/js/FileTransferrer.js b/src/js/FileTransferrer.js
index 6cc90f1..4157293 100644
--- a/src/js/FileTransferrer.js
+++ b/src/js/FileTransferrer.js
@@ -105,7 +105,7 @@ class FileTransferrer {
                 }
 
                 // update file transfer progress
-                fileTransfer.progress = Math.min(100, Math.ceil(fileChunk.offset + fileChunk.length / fileTransfer.filesize * 100));
+                fileTransfer.progress = Math.min(100, Math.ceil((fileChunk.offset + fileChunk.length) / fileTransfer.filesize * 100));
 
             } catch(e) {
                 this.log("failed to get file chunk", e);