I ran into this bug (https://debbugs.gnu.org/cgi/bugreport.cgi?bug=21028)
via prettify-symbols-mode, and applying Clément's patch fixed the issue.

I'm running GNU Emacs 24.5.1 (x86_64-pc-linux-gnu, GTK+ Version 3.18.9)
 of 2016-04-17 on lgw01-04, modified by Debian
Windowing system distributor `The X.Org Foundation', version 11.0.11803000
System Description: Ubuntu 16.04.1 LTS

-Jason