diff --git a/swash/processing/sws_npz.py b/swash/processing/sws_npz.py
index 7aef1cd..06c02c6 100644
--- a/swash/processing/sws_npz.py
+++ b/swash/processing/sws_npz.py
@@ -1,7 +1,7 @@
 import argparse
 import configparser
 import logging
-from multiprocessing import ThreadPool
+from multiprocessing.pool import Pool
 import pathlib
 
 import numpy as np
@@ -39,7 +39,7 @@ var = {
 }
 
 inp.mkdir(exist_ok=True)
-with ThreadPool() as pool:
+with Pool() as pool:
     pool.map(
         lambda name, f: np.save(
             inp.joinpath(name), f(sws_out.joinpath(name).with_suffix(".dat"))