Running scons fails

With the these commands,

$ git clone https://github.com/simonask/w.git --recursive
$ cd w
$ scons -j8

I get the following error message from scons:

scons: Reading SConscript files ...
TypeError: 'builtin_function_or_method' object has no attribute '__getitem__':
  File "<PATH_TO>/w/SConstruct", line 97:
    w_dev = WaywardProgram(env_with_ws, 'w_dev', w_util_sources, rpaths = ['.'])
  File "<PATH_TO>/w/wayward_build.py", line 37:
    libs.extend['event', 'event_pthreads', 'pq', 'unwind']

I'm running Arch linux with Scons 2.3.2.