Pip: could not find a version. No matching distribution found

I’m trying to install Flask-ACL:
https://mikeboers.github.io/Flask-ACL

$ pip search acl | grep -i flask

Flask-ACL (0.0.1) - Access control lists for Flask.
flask-miracle-acl (0.2) - The fabric between the Flask framework and Miracle ACL

Flask-Sandbox (0.1.0)- ACL Route controls for Flask
Flask-SimpleACL (1.2)- Simple ACL extension


$ pip install Flask-ACL

Collecting Flask-ACL
Could not find a version that satisfies the requirement Flask-ACL (from versions: )
No matching distribution found for Flask-ACL

What’s wrong here?

P.S. Pip was upgraded a few minutes ago.

UPDATE:

$ python --version
Python 2.7.3

I’m running it under virtualenv.

pip install -Iv Flask-ACL

Collecting Flask-ACL
1 location(s) to search for versions of Flask-ACL:
* https://pypi.python.org/simple/flask-acl/
Getting page https://pypi.python.org/simple/flask-acl/
Looking up "https://pypi.python.org/simple/flask-acl/" in the cache
Current age based on date: 507
Freshness lifetime from max-age: 600
Freshness lifetime from request max-age: 600
The response is "fresh", returning cached response
600 > 507
Analyzing links from page https://pypi.python.org/simple/flask-acl/
Could not find a version that satisfies the requirement Flask-ACL (from versions: )

Cleaning up…
No matching distribution found for Flask-ACL

As I can see, there is no such package on Pypi:

https://pypi.python.org/simple/flask-acl/

but this one exist:

https://pypi.python.org/pypi/Flask-ACL

What is wrong with my pip?