shutil.Error while installing hooks (alpine docker, musl)

We are moving to docker based CI and I'm trying to build a pre-commit testing container that is pre-populated with our hooks. Could you help me diagnose the cause of this failure? When the hooks try to install I get:

Initialized empty Git repository in /root/pre-commit/.git/
[INFO] Initializing environment for https://github.com/pre-commit/pre-commit-hooks.git.
[INFO] Installing environment for https://github.com/pre-commit/pre-commit-hooks.git.
[INFO] Once installed this environment will be reused.
[INFO] This may take a few minutes...
An unexpected error has occurred: CalledProcessError: Command: ('/root/.cache/pre-commit/repojfihsrn1/py_env-python3.5/bin/python3.5', '/root/.cache/pre-commit/repojfihsrn1/py_env-python3.5/bin/pip', 'install', '.')
Return code: 2
Expected return code: 0
Output:
    Processing /root/.cache/pre-commit/repojfihsrn1

Stack trace attached
github-issue-655-trace.txt