I updated Freetype from 2.5.0 to 2.5.1 via Homebrew, and uninstalled and reinstalled Matplotlib 1.3.1, but it failed to build because it includes /usr/X11/include/ft2build.h, which includes freetype/config/ftheader.h, but the Freetype changelog (and ft2build.h itself) mentions including freetype2/config/ftheader.h instead.

I don't know how ReportLab and Pillow skipped including this header and built successfully with Freetype support in the same environment.