Building failed because of "Package x11 not found"

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http://askubuntu.com – I am trying to build an application I am making into launchpad for my PPA, and, while it builds the DEB just fine locally, it fails in launchpad. The build log complains that Project ERROR: Package x11 not found while I totally build-depend on libx11-dev, and a package named x11 does not exist! Here's the PPA : https://launchpad.net/~hakermania/+archive/macropolo/+packages The buildlog (i386): https://launchpadlibrarian.net/115106043/buildlog_ubuntu-precise-i386.ma... Can you please solve this mystery? (HowTos)