Mybb Forum index error

[Teal]

I'm using all default files but whenever i try going to my home page i get this error
"Fatal error: Call to undefined function my_unserialize() in /home/a4250975/public_html/index.php on line 348"

Can anyone help me fix this problem?

notes: iv'e tried re-uploading index.php already

[Yaldaram]

Upload ./inc/functions.php file from the fresh MyBB download.

[Teal]

thank you for the help.