diff --git a/Makefile.pre.in b/Makefile.pre.in
index ee1cd4a0280..5602c165463 100644
--- a/Makefile.pre.in
+++ b/Makefile.pre.in
@@ -1035,7 +1035,7 @@ buildbottest:	build_all platform
 		-@if which pybuildbot.identify >/dev/null 2>&1; then \
 			pybuildbot.identify "CC='$(CC)'" "CXX='$(CXX)'"; \
 		fi
-		$(TESTRUNNER) -j 1 -u all -W --slowest --timeout=$(TESTTIMEOUT) $(TESTOPTS)
+		$(TESTRUNNER) -j 1 -u all -W --slowest --fail-env-changed --timeout=$(TESTTIMEOUT) $(TESTOPTS)
 
 QUICKTESTOPTS=	$(TESTOPTS) -x test_subprocess test_io test_lib2to3 \
 		test_multibytecodec test_urllib2_localnet test_itertools \
diff --git a/Tools/buildbot/test.bat b/Tools/buildbot/test.bat
index 0b3a3091c1e..40ffc7efdd2 100644
--- a/Tools/buildbot/test.bat
+++ b/Tools/buildbot/test.bat
@@ -16,4 +16,4 @@ if "%1"=="+q" (set rt_opts=%rt_opts:-q=%) & shift & goto CheckOpts
 if NOT "%1"=="" (set regrtest_args=%regrtest_args% %1) & shift & goto CheckOpts
 
 echo on
-call "%here%..\..\PCbuild\rt.bat" %rt_opts% -uall -rwW --slowest --timeout=1200 %regrtest_args%
+call "%here%..\..\PCbuild\rt.bat" %rt_opts% -uall -rwW --slowest --timeout=1200 --fail-env-changed %regrtest_args%