pipenvでpythonのバージョン指定がしたいのですが↓のようにFailed creating virtual environmentになってしまいます。なぜでしょうか？

[vagrant@localhost mypy]$ pipenv --python 3.7
Virtualenv already exists!
Removing existing virtualenv...
Creating a virtualenv for this project...
Pipfile: /home/vagrant/myreact/hw/src/python/Python-3.7.3/mypy/Pipfile
Using /usr/local/bin/python3.7 (3.7.3) to create virtualenv...
⠼ Creating virtual environment...Running virtualenv with interpreter /usr/local/bin/python3.7

✘ Failed creating virtual environment
[pipenv.exceptions.VirtualenvCreationException]:   File "/usr/lib/python2.7/site-packages/pipenv/cli/command.py", line 208, in cli
[pipenv.exceptions.VirtualenvCreationException]:       clear=state.clear,
[pipenv.exceptions.VirtualenvCreationException]:   File "/usr/lib/python2.7/site-packages/pipenv/core.py", line 574, in ensure_project
[pipenv.exceptions.VirtualenvCreationException]:       pypi_mirror=pypi_mirror,
[pipenv.exceptions.VirtualenvCreationException]:   File "/usr/lib/python2.7/site-packages/pipenv/core.py", line 536, in ensure_virtualenv
[pipenv.exceptions.VirtualenvCreationException]:       pypi_mirror=pypi_mirror,
[pipenv.exceptions.VirtualenvCreationException]:   File "/usr/lib/python2.7/site-packages/pipenv/core.py", line 506, in ensure_virtualenv
[pipenv.exceptions.VirtualenvCreationException]:       python=python, site_packages=site_packages, pypi_mirror=pypi_mirror
[pipenv.exceptions.VirtualenvCreationException]:   File "/usr/lib/python2.7/site-packages/pipenv/core.py", line 935, in do_create_virtualenv
[pipenv.exceptions.VirtualenvCreationException]:       extra=[crayons.blue("{0}".format(c.err)),]
[pipenv.exceptions.VirtualenvCreationException]: Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/virtuale

[vagrant@localhost mypy]$ python3.7 -V
Python 3.7.3

['', '/usr/local/lib/python37.zip', '/usr/local/lib/python3.7', '/usr/local/lib/python3.7/lib-dynload', '/usr/local/lib/python3.7/site-packages']
>>> exit()

追記
Pipfileのrequiresに3.7を指定したり、削除したりしましたが駄目でした。PATHは通っています。

[vagrant@localhost mypy]$ which python3.7
/usr/local/bin/python3.7
[vagrant@localhost mypy]$ echo $PATH
/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/home/vagrant/.local/bin:/home/vagrant/bin
[vagrant@localhost mypy]$