diff --git a/news/8214.bugfix b/news/8214.bugfix
new file mode 100644
index 00000000000..1dc5cd79d11
--- /dev/null
+++ b/news/8214.bugfix
@@ -0,0 +1 @@
+Fix installing packages which have a pyproject.toml when enum34 is installed.
diff --git a/news/8214.removal b/news/8214.removal
new file mode 100644
index 00000000000..31f3089493d
--- /dev/null
+++ b/news/8214.removal
@@ -0,0 +1,2 @@
+Removes the ability to run pip via ``python src/pip/`` from a checkout without
+setting PYTHONPATH first.
diff --git a/src/pip/__main__.py b/src/pip/__main__.py
index 7c2505fa5bd..a529758b395 100644
--- a/src/pip/__main__.py
+++ b/src/pip/__main__.py
@@ -18,7 +18,10 @@
     # Resulting path is the name of the wheel itself
     # Add that to sys.path so we can import pip
     path = os.path.dirname(os.path.dirname(__file__))
-    sys.path.insert(0, path)
+    # __package__ could have also been the empty string if pip was invoked
+    # with the path to the pip directory.  ie: as python /path/to/pip/.
+    if path.endswith('.whl'):
+        sys.path.insert(0, path)
 
 from pip._internal.cli.main import main as _main  # isort:skip # noqa