/etc/apt/sources.list:

deb http://packages.dotdeb.org squeeze all
deb-src http://packages.dotdeb.org squeeze all
deb http://packages.dotdeb.org squeeze-php54 all
deb-src http://packages.dotdeb.org squeeze-php54 all
# wget http://www.dotdeb.org/dotdeb.gpg
# cat dotdeb.gpg | sudo apt-key add -