diff --git a/mlair/run_modules/pre_processing.py b/mlair/run_modules/pre_processing.py
index 68d1b7cba78fbab54f4db2b969b92c9d703acc4a..13a4b38184ea3c00c9cf5990c35c6d7bdcb6225d 100644
--- a/mlair/run_modules/pre_processing.py
+++ b/mlair/run_modules/pre_processing.py
@@ -216,7 +216,7 @@ class PreProcessing(RunEnvironment):
         valid_stations = []
         kwargs = self.data_store.create_args_dict(data_handler.requirements(), scope=set_name)
 
-        if os.cpu_count() > 1:  # parallel solution
+        if multiprocessing.cpu_count() > 1:  # parallel solution
             logging.info("use parallel validate station approach")
             pool = multiprocessing.Pool()
             output = [