--- a/python/mozbuild/mozbuild/virtualenv.py
+++ b/python/mozbuild/mozbuild/virtualenv.py
@@ -235,7 +235,7 @@
         if os.path.islink(venv_python):
             os.remove(venv_python)
 
-        args = [python, self.virtualenv_script_path,
+        args = [python, "-m" "virtualenv",
                 # Without this, virtualenv.py may attempt to contact the outside
                 # world and search for or download a newer version of pip,
                 # setuptools, or wheel. This is bad for security, reproducibility,
@@ -438,7 +438,7 @@
                 handle_package(package)
 
             sitecustomize = os.path.join(
-                os.path.dirname(os.__file__), 'sitecustomize.py')
+                os.path.dirname(sys.executable), 'sitecustomize.py')
             with open(sitecustomize, 'w') as f:
                 f.write(
                     '# Importing mach_bootstrap has the side effect of\n'