Unbound prefix error in xarco file

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I am getting an unbound prefix error when I try to use an xarco macro. I do have the xmlns:xarco defined however. This is my xarco file:

<?xml version="1.0"?>
<robot xmlns:xacro="[link to xarco wiki]" name="flexible">
  <xacro:macro name="test_macro" >
    <test name="x"/>
  </xacro:macro>

  <xarco:test_macro/>
</robot>

And this is the error I am getting:

Expat parsing error.  Check that:
 - Your XML is correctly formed
 - You have the xacro xmlns declaration: xmlns:xacro="[link to xarco wiki]"

Traceback (most recent call last):
  File "/opt/ros/hydro/share/xacro/xacro.py", line 60, in <module>
    xacro.main()
  File "/opt/ros/hydro/lib/python2.7/dist-packages/xacro/__init__.py", line 571, in main
    doc = parse(f)
  File "/usr/lib/python2.7/xml/dom/minidom.py", line 1920, in parse
    return expatbuilder.parse(file)
  File "/usr/lib/python2.7/xml/dom/expatbuilder.py", line 928, in parse
    result = builder.parseFile(file)
  File "/usr/lib/python2.7/xml/dom/expatbuilder.py", line 207, in parseFile
    parser.Parse(buffer, 0)
xml.parsers.expat.ExpatError: unbound prefix: line 7, column 6

Any help would be appreciated.