diff --git a/nrrd/reader.py b/nrrd/reader.py
index cdf2e11..be30286 100644
--- a/nrrd/reader.py
+++ b/nrrd/reader.py
@@ -367,7 +367,7 @@ def read_data(header, fh=None, filename=None, index_order='F'):
         fh = open(data_filename, 'rb')
 
     # Get the total number of data points by multiplying the size of each dimension together
-    total_data_points = header['sizes'].prod()
+    total_data_points = header['sizes'].prod(dtype=np.int64)
 
     # Skip the number of lines requested when line_skip >= 0
     # Irrespective of the NRRD file having attached/detached header
diff --git a/nrrd/tests/test_reading.py b/nrrd/tests/test_reading.py
index 2551a97..4280496 100644
--- a/nrrd/tests/test_reading.py
+++ b/nrrd/tests/test_reading.py
@@ -412,16 +412,18 @@ def test_invalid_endian(self):
             with self.assertRaisesRegex(nrrd.NRRDError, 'Invalid endian value in header: "fake"'):
                 nrrd.read_data(header, fh, RAW_NRRD_FILE_PATH)
 
-
     def test_invalid_index_order(self):
         with self.assertRaisesRegex(nrrd.NRRDError, 'Invalid index order'):
             nrrd.read(RAW_NRRD_FILE_PATH, index_order=None)
 
+
 class TestReadingFunctionsFortran(TestReadingFunctions, unittest.TestCase):
     index_order = 'F'
 
+
 class TestReadingFunctionsC(TestReadingFunctions, unittest.TestCase):
     index_order = 'C'
 
+
 if __name__ == '__main__':
     unittest.main()