diff --git a/js/script.js b/js/script.js
index efd7b66..8ba504a 100644
--- a/js/script.js
+++ b/js/script.js
@@ -300,9 +300,9 @@ async function clickProgram() {
       const progressBar = progress[file].querySelector("div");
       await espStub.flashData(
         contents,
-        (bytesWritten) => {
+        (bytesWritten, totalBytes) => {
           progressBar.style.width =
-            Math.floor((bytesWritten / contents.byteLength) * 100) + "%";
+            Math.floor((bytesWritten / totalBytes) * 100) + "%";
         },
         offset
       );
diff --git a/src/esp_loader.ts b/src/esp_loader.ts
index 5275327..e375494 100644
--- a/src/esp_loader.ts
+++ b/src/esp_loader.ts
@@ -618,7 +618,7 @@ export class ESPLoader extends EventTarget {
         ? Math.round((block.length * uncompressedFilesize) / compressedFilesize)
         : block.length;
       position += flashWriteSize;
-      updateProgress(written, filesize);
+      updateProgress(written, Math.ceil(filesize / flashWriteSize) * flashWriteSize);
     }
     this.logger.log(
       "Took " + (Date.now() - stamp) + "ms to write " + filesize + " bytes"