Make argparse dependency unconditional.
diff --git a/acme/setup.py b/acme/setup.py
index f169f59a70b..48210108a87 100644
--- a/acme/setup.py
+++ b/acme/setup.py
@@ -8,6 +8,7 @@
 
 # Please update tox.ini when modifying dependency version requirements
 install_requires = [
+    'argparse',
     # load_pem_private/public_key (>=0.6)
     # rsa_recover_prime_factors (>=0.8)
     'cryptography>=0.8',
@@ -30,8 +31,6 @@
 # Keep in sync with conditional_requirements.py.
 if sys.version_info < (2, 7):
     install_requires.extend([
-        # only some distros recognize stdlib argparse as already satisfying
-        'argparse',
         'mock<1.1.0',
     ])
 else:
diff --git a/setup.py b/setup.py
index 0c47b973f60..8ce4c51c946 100644
--- a/setup.py
+++ b/setup.py
@@ -36,6 +36,7 @@ def read_file(filename, encoding='utf8'):
 # https://github.com/pypa/pip/issues/988 for more info.
 install_requires = [
     'acme=={0}'.format(version),
+    'argparse',
     # We technically need ConfigArgParse 0.10.0 for Python 2.6 support, but
     # saying so here causes a runtime error against our temporary fork of 0.9.3
     # in which we added 2.6 support (see #2243), so we relax the requirement.
@@ -58,8 +59,6 @@ def read_file(filename, encoding='utf8'):
 # Keep in sync with conditional_requirements.py.
 if sys.version_info < (2, 7):
     install_requires.extend([
-        # only some distros recognize stdlib argparse as already satisfying
-        'argparse',
         'mock<1.1.0',
     ])
 else:

The primary motivation is to avoid a branch, giving bugs one fewer place to hide. But, as a bonus, more people get a more bugfixed version of argparse. (To use the example from the argparse docs, people stuck on Python 3.2.3 can get bugfixes that made it into the stdlib only in 3.2.4.)
