diff --git a/lib/DataHarmonizer.js b/lib/DataHarmonizer.js
index af67f3c7..26c09816 100644
--- a/lib/DataHarmonizer.js
+++ b/lib/DataHarmonizer.js
@@ -6,7 +6,7 @@ import 'jquery-ui-bundle';
 import 'jquery-ui/dist/themes/base/jquery-ui.css';
 
 import i18next from 'i18next';
-import { utils as XlsxUtils, read as xlsxRead } from 'xlsx/xlsx.mjs';
+import { utils as XlsxUtils, read as xlsxRead } from 'xlsx/xlsx.js';
 import { renderContent, urlToClickableAnchor } from '@/lib/utils/content';
 import { readFileAsync, updateSheetRange } from '@/lib/utils/files';
 import { findSlotNamesForClass } from '@/lib/utils/templates';
diff --git a/lib/utils/files.js b/lib/utils/files.js
index 6d43b335..1d4b7134 100644
--- a/lib/utils/files.js
+++ b/lib/utils/files.js
@@ -1,4 +1,4 @@
-import { utils as XlsxUtils, writeFile } from 'xlsx/xlsx.mjs';
+import { utils as XlsxUtils, writeFile } from 'xlsx/xlsx.js';
 import { saveAs } from 'file-saver';
 
 /**