diff -ur astropy-0.3.2/astropy/io/fits/hdu/base.py astropy-0.3.2.checksum/astropy/io/fits/hdu/base.py

--- astropy-0.3.2/astropy/io/fits/hdu/base.py	2014-05-19 15:50:15.540882206 +0200

+++ astropy-0.3.2.checksum/astropy/io/fits/hdu/base.py	2014-05-19 15:51:32.084487630 +0200

@@ -1581,8 +1581,8 @@

         hi = sum32 >> u16

         lo = sum32 & uFFFF

-        hi += np.add.reduce(bytes[0::2])

-        lo += np.add.reduce(bytes[1::2])

+        hi += np.add.reduce(bytes[0::2], dtype=np.uint64)

+        lo += np.add.reduce(bytes[1::2], dtype=np.uint64)

         if (bytes.nbytes // 2) % 2:

             lo += last << u8

diff -ur astropy-0.3.2/astropy/io/fits/tests/test_checksum.py astropy-0.3.2.checksum/astropy/io/fits/tests/test_checksum.py

--- astropy-0.3.2/astropy/io/fits/tests/test_checksum.py	2014-05-19 15:50:15.549882277 +0200

+++ astropy-0.3.2.checksum/astropy/io/fits/tests/test_checksum.py	2014-05-19 15:52:39.844024043 +0200

@@ -42,7 +42,7 @@

         hdul.close()

     def test_image_create(self):

-        n = np.arange(100)

+        n = np.arange(100, dtype=np.int64)

         hdu = fits.PrimaryHDU(n)

         hdu.writeto(self.temp('tmp.fits'), clobber=True, checksum=True)

         with fits.open(self.temp('tmp.fits'), checksum=True) as hdul:

@@ -57,7 +57,7 @@

                 assert hdul[0].header['DATASUM'] == '4950'

     def test_nonstandard_checksum(self):

-        hdu = fits.PrimaryHDU(np.arange(10.0 ** 6))

+        hdu = fits.PrimaryHDU(np.arange(10.0 ** 6, dtype=np.float64))

         hdu.writeto(self.temp('tmp.fits'), clobber=True,

                     checksum='nonstandard')

         del hdu