diff --git a/roles/tox/library/tox_install_sibling_packages.py b/roles/tox/library/tox_install_sibling_packages.py
index cbf81818c..b887f4179 100644
--- a/roles/tox/library/tox_install_sibling_packages.py
+++ b/roles/tox/library/tox_install_sibling_packages.py
@@ -109,8 +109,7 @@ def get_sibling_python_packages(projects, tox_python):
             # package name is.
             package_name = subprocess.check_output(
                 [os.path.abspath(tox_python), 'setup.py', '--name'],
-                cwd=os.path.abspath(root),
-                stderr=subprocess.STDOUT).decode('utf-8')
+                cwd=os.path.abspath(root)).decode('utf-8')
             if package_name:
                 package_name = package_name.strip()
                 packages[package_name] = root