--- a/src/lxml/tests/test_threading.py	2018-11-28 23:02:48.320893543 +0530
+++ b/src/lxml/tests/test_threading.py	2018-11-28 23:05:49.620897165 +0530
@@ -153,9 +153,9 @@ class ThreadingTestCase(HelperTestCase):
             self.assertTrue(len(log))
             if last_log is not None:
                 self.assertEqual(len(last_log), len(log))
-            self.assertEqual(4, len(log))
+            self.assertTrue(len(log) >= 2, len(log))
             for error in log:
-                self.assertTrue(':ERROR:XSLT:' in str(error))
+                self.assertTrue(':ERROR:XSLT:' in str(error), str(error))
             last_log = log
 
     def test_thread_xslt_apply_error_log(self):