This crash seems to be related to an issue which was reported in July on Fedora, see #60, #61, bug report 13920 and the forum discussion starting here.
The fix for Fedora doesn’t seem to work, as no TypeError is raised. I just released an update, v0.1.169, which always uses my fallback implementation of Pango.extents_to_pixels(). Please report back if the latest version works for you.