diff --git a/Lib/fontTools/misc/py23_test.py b/Lib/fontTools/misc/py23_test.py
index 867945f01..05780d291 100644
--- a/Lib/fontTools/misc/py23_test.py
+++ b/Lib/fontTools/misc/py23_test.py
@@ -37,7 +37,8 @@ class OpenFuncWrapperTest(unittest.TestCase):
 			with open(datafile, 'rb') as infile, \
 					tempfile.NamedTemporaryFile(delete=False) as outfile:
 				check_call(
-					[sys.executable, script], stdin=infile, stdout=outfile)
+					[sys.executable, script], stdin=infile, stdout=outfile,
+					env={"PYTHONPATH": ":".join(sys.path)})
 			result = not filecmp.cmp(infile.name, outfile.name, shallow=False)
 		finally:
 			os.remove(script)