diff --git a/tests/run-tests.py b/tests/run-tests.py
index afab133238..86b2fe5457 100755
--- a/tests/run-tests.py
+++ b/tests/run-tests.py
@@ -712,9 +712,11 @@ def run_tests(pyb, tests, args, result_dir, num_threads=1):
             with open(test_file_expected, "rb") as f:
                 output_expected = f.read()
         else:
+            # CIRCUITPY: set language & make sure testlib is available for `skip_ok`.
+            e = {"PYTHONPATH": "testlib", "PATH": os.environ["PATH"], "LANG": "en_US.UTF-8"}
             # run CPython to work out expected output
             try:
-                output_expected = subprocess.check_output(CPYTHON3_CMD + [test_file])
+                output_expected = subprocess.check_output(CPYTHON3_CMD + [test_file], env=e)
                 if args.write_exp:
                     with open(test_file_expected, "wb") as f:
                         f.write(output_expected)
diff --git a/tests/skip_if.py b/tests/testlib/skip_if.py
similarity index 100%
rename from tests/skip_if.py
rename to tests/testlib/skip_if.py