My np.fft.rfftn returns a wrongly shaped array:

Enthought Canopy Python 2.7.6 | 64-bit | (default, Sep 15 2014, 17:43:19)
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
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>>> import numpy as np
>>> grid = np.random.random((8,8,8))
>>> np.fft.rfftn(grid).shape
(8, 8, 8)

The shape should be (8, 8, 5) in this case. What could be causing this behavior? Numpy version is 1.8.1. I'm running on Mac OS X 10.9 (Mavericks).