Cython not recognizing Numpy types

Question

I'm learning Cython and can't get a simple example to work. I have the following code to compute a sigmoid function:

import numpy as np
cimport numpy as cnp

cdef inline cnp.float32_t _sigmoid(cnp.float32_t x):
    return 1/(1 + np.exp(-x))

Compiling gives an error 'float32_t' is not a type identifier

What am I missing?