diff --git a/conftest.py b/conftest.py
index abb0c0f52757e4b2228d7d48e3dc07e08b302841..b63d3efb33f5b2c02185f16e8753231d1853e66c 100644
--- a/conftest.py
+++ b/conftest.py
@@ -66,5 +66,5 @@ def default_session_fixture(request):
 
     # request.addfinalizer(unpatch)
 
-    with mock.patch("multiprocessing.cpu_count", return_value=1):
+    with mock.patch("psutil.cpu_count", return_value=1):
         yield
diff --git a/mlair/run_modules/pre_processing.py b/mlair/run_modules/pre_processing.py
index 11d732760d99a8ac1c9b94e6e87378f21fe8b825..c7d7f920743cd2973870bdecde860fe9fa57ae37 100644
--- a/mlair/run_modules/pre_processing.py
+++ b/mlair/run_modules/pre_processing.py
@@ -245,7 +245,7 @@ class PreProcessing(RunEnvironment):
 
         max_process = self.data_store.get("max_number_multiprocessing")
         n_process = min([psutil.cpu_count(logical=False), len(set_stations), max_process])  # use only physical cpus
-        if n_process > 1 and use_multiprocessing:  # parallel solution
+        if n_process > 1 and use_multiprocessing is True:  # parallel solution
             logging.info("use parallel validate station approach")
             pool = multiprocessing.Pool(n_process)
             logging.info(f"running {getattr(pool, '_processes')} processes in parallel")
diff --git a/test/test_run_modules/test_pre_processing.py b/test/test_run_modules/test_pre_processing.py
index 5ae64bf3d535e72d9361394741ed8b8094091b1d..0f2ee7a10fd2e3190c0b66da558626747d4c03c9 100644
--- a/test/test_run_modules/test_pre_processing.py
+++ b/test/test_run_modules/test_pre_processing.py
@@ -109,7 +109,7 @@ class TestPreProcessing:
         assert caplog.record_tuples[-1] == ('root', 20, PyTestRegex(r'run for \d+:\d+:\d+ \(hh:mm:ss\) to check 6 '
                                                                     r'station\(s\). Found 5/6 valid stations.'))
 
-    @mock.patch("multiprocessing.cpu_count", return_value=3)
+    @mock.patch("psutil.cpu_count", return_value=3)
     @mock.patch("multiprocessing.Pool", return_value=multiprocessing.Pool(3))
     def test_validate_station_parallel(self, mock_pool, mock_cpu, caplog, obj_with_exp_setup):
         pre = obj_with_exp_setup