No such file or directory ffmpeg

I am trying to concat 2 mp3 files into one.

I have created a concat.txt file with for example the following in the same folder as the files I’m trying to concat exist:

concat.txt

file 'some-song1.mp3'
file 'some-song2.mp3'

Those mp3 files are in the same directory as this txt file and I’m already cd’d into this directory. This directory lives on a volume.

When I run the following:

ffmpeg -f concat -i concat.txt -c copy combined.mp3

I get:

Impossible to open 'some-song1.mp3'
concat.txt: No such file or directory 

I’m on Mac OS X