Matplotlib legend fontsize

Am I using the fontsize argument incorrectly in the following code?
According to the documentation, this should be a valid keyword argument.

import pylab
pylab.plot(range(5), label='test')
pylab.legend(fontsize='small') 
pylab.show()

Traceback:

Traceback (most recent call last):
  File "test_label.py", line 6, in <module>
    pylab.legend(fontsize='small')
  File "C:swframepython-V01-01libsite-packagesmatplotlibpyplot.py", line 2
791, in legend
    ret =  gca().legend(*args, **kwargs)
  File "C:swframepython-V01-01libsite-packagesmatplotlibaxes.py", line 447
5, in legend
    self.legend_ = mlegend.Legend(self, handles, labels, **kwargs)
TypeError: __init__() got an unexpected keyword argument 'fontsize'

Python: 2.7, Matplotlib: 1.1.0

Edit: Note, I am not looking for alternative ways to set the font size. I want to know why this goes wrong.