Description of problem:
Not sure but I think I tried to install an i686 package on my x86_64 system.

Version-Release number of selected component:
dnf-0.4.10-1.fc20

Additional info:
reporter:       libreport-2.1.10
cmdline:        /usr/bin/python /bin/dnf install tinyxml-devel tinyxml-devel.i?86
dso_list:       python-hawkey-0.4.7-1.fc20.x86_64
executable:     /bin/dnf
kernel:         3.11.10-301.fc20.x86_64
runlevel:       N 5
type:           Python
uid:            0

Truncated backtrace:
__init__.py:183:install:ArchException: Used arch is unknown.

Traceback (most recent call last):
  File "/bin/dnf", line 35, in <module>
    main.user_main(sys.argv[1:], exit_code=True)
  File "/usr/lib/python2.7/site-packages/dnf/cli/main.py", line 240, in user_main
    errcode = main(args)
  File "/usr/lib/python2.7/site-packages/dnf/cli/main.py", line 63, in main
    return _main(base, args)
  File "/usr/lib/python2.7/site-packages/dnf/cli/main.py", line 122, in _main
    cli.run()
  File "/usr/lib/python2.7/site-packages/dnf/cli/cli.py", line 1456, in run
    return self.command.run(self.base.extcmds)
  File "/usr/lib/python2.7/site-packages/dnf/cli/commands.py", line 299, in run
    return self.base.installPkgs(extcmds)
  File "/usr/lib/python2.7/site-packages/dnf/cli/cli.py", line 336, in installPkgs
    self.install(arg)
  File "/usr/lib/python2.7/site-packages/dnf/base.py", line 1518, in install
    self._goal.install(select=sltr)
  File "/usr/lib64/python2.7/site-packages/hawkey/__init__.py", line 157, in tweaked_fn
    return fn(self, *args, **kwargs)
  File "/usr/lib64/python2.7/site-packages/hawkey/__init__.py", line 183, in install
    super(Goal, self).install(*args, **kwargs)
ArchException: Used arch is unknown.

Local variables in innermost frame:
self: <hawkey.Goal object at 0x29a3af0>
args: ()
kwargs: {'select': <dnf.selector.Selector object at 0x29a3f00>}