Context including sample code and a test file: https://github.com/SheetJS/js-xlsx/issues/1612 The Window2 situation is unclear: - Excel accepts files without Window2 records - The [official Binary File Format Validator](https://www.microsoft.com/en-us/download/details.aspx?id=26794) accepts files without Window2 records - The [official specification](https://docs.microsoft.com/en-us/openspecs/office_file_formats/ms-xls/a1b3d8b4-7442-41fd-9c57-bbd2a6394082) claims it is required. The issue here is that we write files without the Window2 record, based on the fact that Excel and the BFFValidator program both accept them without error. However Apache POI is apparently erroring. Since Excel does not require it and since the official validator does not require it, the Window2 record should probably be treated as optional