LoadError enc/trans/single_byte.so

I receive the following error when attempting to do string.encode("UTF-8") with a non-ascii character.

LoadError: dlopen(enc/trans/single_byte.so, 9): image not found - enc/trans/single_byte.so

Unlike the answer here, it appears that this file does not exist in my ruby install, or anywhere else on the system for that matter. I'm running ruby 2.1.7 and bundler 1.10.6, running on Mac OSX 10.11.5. I tried reinstalling ruby (using RVM) with no success.

Should this file exist, and if so what do I need to install?