.xlsx downloading issue

I have generated .xlsx reports on server, and page with direct links to these reports. When user clicks a link, report file is downloaded, but file extension is changed to .xls. Therefore, I can't open file correctly, only after changing of extension.

Problem occurs in IE, Firefox correctly downloads file, and Chrome save开发者_StackOverflow中文版s file with name "File.xlsx.xls"

What can cause such behaviour? Any help appreciated.

---

Problem fixed with setting of mime-type "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet" for .xlsx files