diff -Nurp a/pip/_vendor/pep517/wrappers.py b/pip/_vendor/pep517/wrappers.py
--- a/pip/_vendor/pep517/wrappers.py	2019-07-30 20:02:13.000000000 +0800
+++ b/pip/_vendor/pep517/wrappers.py	2020-04-24 17:23:35.764905235 +0800
@@ -10,6 +10,9 @@ from . import compat
 
 _in_proc_script = pjoin(dirname(abspath(__file__)), '_in_process.py')
 
+if not os.path.isfile(_in_proc_script):
+    _in_proc_script = pjoin(dirname(abspath(__file__)), '_in_process.pyc')
+
 
 @contextmanager
 def tempdir():