For the longest of times, I’ve been getting an error or warning message from Brew whenever I used any of its commands. It didn’t cause any issues with using it, but it was just annoying as hell:

Ignoring bigdecimal-1.3.4 because its extensions are not built.  Try: gem pristine bigdecimal --version 1.3.4

As you can probably tell from the error message, its not actually anything to do with Brew itself, rather the language its built on: Ruby.

According to this issue on GitHub, most people started seeing this issue after updating to MacOS Mojave.

The recommended steps to solve, were to make sure you have updated XCode tools with xcode-select install (though this should be dealt with through the updater in settings now), and then to just re-install the gem.

The warning message literally tells you how to fix it, but I tried it and it didn’t work. This dingus (me) didn’t read the error message when it didn’t work, which explained that I didn’t have permission to edit the ruby gems directory.

I finally clicked and discovered that you had to use sudo. Duh.

sudo gem pristine bigdecimal --version 1.3.4

After that, I didn’t have any more issues with Brew.

If your system is anything like mine, you’ll probably see a tonne of similar issues with other gems, but I didn’t really want to open that Pandora’s Box.

terminal after resetting the bigdecimal to a pristine state