pipenv: v11.10.1: initial `pipenv install` in existing virtualenv fails

{'implementation_name': 'cpython',
 'implementation_version': '3.6.5',
 'os_name': 'posix',
 'platform_machine': 'x86_64',
 'platform_python_implementation': 'CPython',
 'platform_release': '4.16.3-1-ARCH',
 'platform_system': 'Linux',
 'platform_version': '#1 SMP PREEMPT Thu Apr 19 09:17:56 UTC 2018',
 'python_full_version': '3.6.5',
 'python_version': '3.6',
 'sys_platform': 'linux'}

Expected result

Courtesy Notice: Pipenv found itself running within a virtual environment, so it will automatically use that environment, instead of creating its own for any project. You can set PIPENV_IGNORE_VIRTUALENVS=1 to force pipenv to ignore that environment and create its own instead.
Creating a Pipfile for this project…
Pipfile.lock not found, creating…
Locking [dev-packages] dependencies…
Using pip: -i https://pypi.python.org/simple

                          ROUND 1                           
Current constraints:

Finding the best candidates:

Finding secondary dependencies:
------------------------------------------------------------
Result of round 1: stable, done

Locking [packages] dependencies…
Using pip: -i https://pypi.python.org/simple

                          ROUND 1                           
Current constraints:

Finding the best candidates:

Finding secondary dependencies:
------------------------------------------------------------
Result of round 1: stable, done

Updated Pipfile.lock (625834)!
Installing dependencies from Pipfile.lock (625834)…

Actual result

Courtesy Notice: Pipenv found itself running within a virtual environment, so it will automatically use that environment, instead of creating its own for any project. You can set PIPENV_IGNORE_VIRTUALENVS=1 to force pipenv to ignore that environment and create its own instead.
Creating a Pipfile for this project…
Warning: --system is intended to be used for Pipfile installation, not installation of specific packages. Aborting.
See also: --deploy flag.

Steps to replicate

Requires pipenv v11.10.1. Not reproducible in v11.10.0. In an empty directory, run:

$ virtualenv env
$ source env/bin/activate
$ pipenv install