diff --git a/Makefile b/Makefile
index 4660b5f4..8f596bfa 100644
--- a/Makefile
+++ b/Makefile
@@ -68,7 +68,7 @@ pretest:
 	python scripts/gen_individual_importing_tests.py
 
 TEST_ENV_PATH = "`pwd`:`pwd`/tests/lib"
-TEST_ENV = PYTHONPATH=$(TEST_ENV_PATH) PERL5LIB=$(TEST_ENV_PATH)
+TEST_ENV = PYTHONPATH="$$PYTHONPATH:"$(TEST_ENV_PATH) PERL5LIB="$$PERL5LIB:"$(TEST_ENV_PATH)
 TEST_FILES = tests/style/*.t tests/unit-generated/*.py tests/individually-importing/*.py
 
 define RUN_TESTS