I have a largish cython module that outputs the following warnings every time I import the compiled module. __main__:1: RuntimeWarning: numpy.dtype size changed, may indicate binary incompatibility __main__:1: RuntimeWarning: numpy.flatiter size changed, may indicate binary incompatibility Is this something I should worry about? I've traced this warning gets generated when a `cimport numpy as np` line is processed in my module. When I comment out that line I don't get any warning. To recreate this error I've created a cython with only that line as follows: numpy_test.pyx: cimport numpy as np A barebones setup in `setup.py`: from distutils.core import setup from distutils.extension import Extension from Cython.Distutils import build_ext setup(name='numpy_test', version='tip', cmdclass={'build_ext': build_ext}, ext_modules=[Extension(name="numpy_test", sources=['numpy_test.pyx'])] ) Then I do a local build like this: python setup.py build cd into the build directory: cd build/lib.linux-x86_64-2.6/ verify the .so is there: $ ls numpy_test.so and import it and get the runtime warning: $ python -c "import numpy_test" -c:1: RuntimeWarning: numpy.dtype size changed, may indicate binary incompatibility -c:1: RuntimeWarning: numpy.flatiter size changed, may indicate binary incompatibility I'm running 64 bit Ubuntu 10.04, Python 2.6.6, and Cython 0.15.1. Any help would be greatly appreciated! Rich -- Richard P. Sharp Jr. Lead Software Developer Natural Capital Project Stanford University, U Minnesota, TNC, WWF 371 Serra Mall Stanford, CA 94305 http://www.stanford.edu/~rpsharp/