Getting IOError: [Errno 21] Is a directory error when trying to run PyInstaller

I'm trying to create an executable file for my Python script using PyInstaller. I run in the terminal:

pyinstaller --onefile --windowed ./lab_attendant_emailer.py

From the directory that the python file is in. It starts running for a bit but returns this error.

12 INFO: PyInstaller: 3.1.112 INFO: Python: 2.7.612 INFO: Platform: Linux-3.16.0-67-generic-x86_64-with-Ubuntu-14.04-trusty12 INFO: wrote /home/carsnwd/PycharmProjects/labattendantemailer/lab_attendant_emailer.spec14 INFO: UPX is not available.15 INFO: Extending PYTHONPATH with paths['/home/carsnwd/PycharmProjects/labattendantemailer','/home/carsnwd/PycharmProjects/labattendantemailer']15 INFO: checking Analysis21 INFO: checking PYZ22 INFO: checking PKG25 INFO: Bootloader /usr/local/lib/python2.7/dist-packages/PyInstaller/bootloader/Linux-64bit/run25 INFO: checking EXE25 INFO: Building because name changed25 INFO: Building EXE from out00-EXE.tocTraceback (most recent call last):  File "/usr/local/bin/pyinstaller", line 9, in <module>    load_entry_point('PyInstaller==3.1.1', 'console_scripts', 'pyinstaller')()  File "/usr/local/lib/python2.7/dist-packages/PyInstaller/__main__.py", line 90, in run    run_build(pyi_config, spec_file, **vars(args))  File "/usr/local/lib/python2.7/dist-packages/PyInstaller/__main__.py", line 46, in run_build    PyInstaller.building.build_main.main(pyi_config, spec_file, **kwargs)  File "/usr/local/lib/python2.7/dist-packages/PyInstaller/building/build_main.py", line 755, in main    build(specfile, kw.get('distpath'), kw.get('workpath'), kw.get('clean_build'))  File "/usr/local/lib/python2.7/dist-packages/PyInstaller/building/build_main.py", line 701, in build    exec(text, spec_namespace)  File "<string>", line 28, in <module>  File "/usr/local/lib/python2.7/dist-packages/PyInstaller/building/api.py", line 498, in __init__    self.__postinit__()  File "/usr/local/lib/python2.7/dist-packages/PyInstaller/building/datastruct.py", line 183, in __postinit__    self.assemble()  File "/usr/local/lib/python2.7/dist-packages/PyInstaller/building/api.py", line 575, in assemble    outf = open(self.name, 'wb')IOError: [Errno 21] Is a directory: '/home/carsnwd/PycharmProjects/labattendantemailer/dist/lab_attendant_emailer'

What am I doing wrong?