[Owncloud] PHP mb multibyte error after git update

[Advrk Aplmrkt]

Hello,
I updated ownCloud to the latest version from git to see if the
calendar has been improved, but now get this error when I enter my
ownCloud URL:

"PHP module mb multibyte not installed."

ownCloud was working for me before, so how do I fix this? I have no
idea what the mb multibyte module is or how it should be installed. Is
this a new prerequisite for running ownCloud?

Thanks.