diff --git a/python-waitress.changes b/python-waitress.changes
index 28f9994..fbc28b7 100644
--- a/python-waitress.changes
+++ b/python-waitress.changes
@@ -1,3 +1,11 @@
+-------------------------------------------------------------------
+Wed Jun 17 08:40:18 UTC 2020 - Jacek Tomasiak <jtomasiak@suse.com>
+
+- make sure UTF8 locale is used when runnning tests
+  * Sometimes functional tests executed in python3 failed if stdout was not
+    set to UTF-8. The error message was:
+      ValueError: underlying buffer has been detached
+
 -------------------------------------------------------------------
 Mon May 18 07:25:32 UTC 2020 - Petr Gajdos <pgajdos@suse.com>
 
diff --git a/python-waitress.spec b/python-waitress.spec
index 211e1af..167fa6e 100644
--- a/python-waitress.spec
+++ b/python-waitress.spec
@@ -75,6 +75,9 @@ python3 setup.py build_sphinx && rm build/sphinx/html/.buildinfo
 %check
 # Tests require a network connection
 rm waitress/tests/test_adjustments.py
+# make sure utf8 locale is set or tests could fail with:
+#    ValueError: underlying buffer has been detached
+export LANG=en_US.UTF8
 %python_exec setup.py test
 
 %post