diff --git a/py_tools_ds/processing/progress_mon.py b/py_tools_ds/processing/progress_mon.py
index 62ce5ee46df236bf076708d59c36c427a28c9499..2df428ca63fc271d4a8471a2c6bbde12d423e5d4 100644
--- a/py_tools_ds/processing/progress_mon.py
+++ b/py_tools_ds/processing/progress_mon.py
@@ -99,6 +99,8 @@ class ProgressBar(object):
         self.use_as_cb = use_as_callback
         self.out = out
 
+        self._percdone = list(range(10, 110, 10))
+
     def print_progress(self, percent):
         """Print progress.
 
@@ -108,11 +110,14 @@ class ProgressBar(object):
         :return:
         """
         if self.Timer.timed_out:
-            self.out.flush()
+            if self.out is not None:
+                self.out.flush()
             if self.use_as_cb:
                 # raise a KeyBoardInterrupt instead of a TimeOutError
                 # as this is catchable by gdal.GetLastException()
                 raise KeyboardInterrupt()
+            else:
+                raise TimeoutError(f'No progress for {self.timeout} seconds.')
 
         formatStr = "{0:." + str(self.decimals) + "f}"
         percents = formatStr.format(percent)
@@ -120,17 +125,30 @@ class ProgressBar(object):
         # bar         = '█' * filledLength + '-' * (barLength - filledLength) # this is not compatible to shell console
         bar = '=' * filledLength + '-' * (self.barLength - filledLength)
 
-        # reset the cursor to the beginning of the line and allows to write over what was previously on the line
-        self.out.write('\r')
+        if self.out is not None:
+            # reset the cursor to the beginning of the line and allows to write over what was previously on the line
+            self.out.write('\r')
 
-        # [%s/%s] numberDone
-        suffix = self.suffix if not self.show_elapsed else '%s  => %s' % (self.suffix, self.Timer.elapsed)
-        self.out.write('%s |%s| %s%s %s' % (self.prefix, bar, percents, '%', suffix))
+            # [%s/%s] numberDone
+            suffix = self.suffix if not self.show_elapsed else '%s  => %s' % (self.suffix, self.Timer.elapsed)
+            self.out.write('%s |%s| %s%s %s' % (self.prefix, bar, percents, '%', suffix))
 
-        if percent >= 100.:
-            self.out.write('\n')
+            if percent >= 100.:
+                self.out.write('\n')
 
-        self.out.flush()
+            self.out.flush()
+
+        else:
+            # in some environments, sys.stderr can also be None
+            # pydocs: usually Windows GUI apps that aren’t connected to a console and Python apps started with pythonw
+            try:
+                percnext = self._percdone[0]
+                if percent >= percnext:
+                    print(f'{percents} %')
+                    self._percdone.pop(0)
+
+            except IndexError:  # pragma: no cover
+                pass
 
     def __call__(self, percent01, message, user_data):
         """Allow ProgressBar instances to be callable and thus to be used as callback function, e.g., for GDAL.
diff --git a/tests/test_processing/__init__.py b/tests/test_processing/__init__.py
new file mode 100644
index 0000000000000000000000000000000000000000..e69de29bb2d1d6434b8b29ae775ad8c2e48c5391
diff --git a/tests/test_processing/test_progress_mon.py b/tests/test_processing/test_progress_mon.py
new file mode 100644
index 0000000000000000000000000000000000000000..0589d2f6e4c23587649963ad166fcab9c272176e
--- /dev/null
+++ b/tests/test_processing/test_progress_mon.py
@@ -0,0 +1,61 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+
+# py_tools_ds - A collection of geospatial data analysis tools that simplify standard
+# operations when handling geospatial raster and vector data as well as projections.
+#
+# Copyright (C) 2016-2021
+# - Daniel Scheffler (GFZ Potsdam, daniel.scheffler@gfz-potsdam.de)
+# - Helmholtz Centre Potsdam - GFZ German Research Centre for Geosciences Potsdam,
+#   Germany (https://www.gfz-potsdam.de/)
+#
+# This software was developed within the context of the GeoMultiSens project funded
+# by the German Federal Ministry of Education and Research
+# (project grant code: 01 IS 14 010 A-C).
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""
+test_progress_mon
+-----------------
+
+Tests for `py_tools_ds.processing.progress_mon` module.
+"""
+
+import unittest
+from time import sleep
+
+from py_tools_ds.processing.progress_mon import ProgressBar
+
+
+class Test_ProgressBar(unittest.TestCase):
+    def test_print_progress(self):
+        bar = ProgressBar(prefix='\tprogress:')
+        for i in range(100):
+            bar.print_progress((i + 1) / 100 * 100)
+
+    def test_timeout(self):
+        with self.assertRaises(TimeoutError):
+            bar = ProgressBar(prefix='\tprogress:', timeout=0.1)
+            for i in range(5):
+                bar.print_progress((i + 1) / 5 * 100)
+                sleep(0.2)
+
+    def test_stderr_is_none(self):
+        bar = ProgressBar(prefix='\tprogress:', out=None)
+        for i in range(73):
+            bar.print_progress((i + 1) / 73 * 100)
+
+
+if __name__ == '__main__':
+    unittest.main()