diff --git a/tox.ini b/tox.ini
index eabdf28c0..c7a41f520 100644
--- a/tox.ini
+++ b/tox.ini
@@ -28,8 +28,6 @@ deps =
 
     # mitmproxy does not support PyPy
     mitmproxy; implementation_name != "pypy"
-setenv =
-    COVERAGE_CORE=sysmon
 passenv =
     S3_TEST_FILE_URI
     AWS_ACCESS_KEY_ID