diff --git a/test/utils.py b/test/utils.py
index 609ab9d7..1c2733c6 100644
--- a/test/utils.py
+++ b/test/utils.py
@@ -33,7 +33,7 @@ def cibuildwheel_get_build_identifiers(project_path, env=None):
     for the current platform.
     '''
     cmd_output = subprocess.check_output(
-        [sys.executable, '-m', 'cibuildwheel', '--print-build-identifiers', project_path],
+        [sys.executable, '-m', 'cibuildwheel', '--print-build-identifiers', str(project_path)],
         universal_newlines=True,
         env=env,
     )