diff --git a/google_auth_oauthlib/flow.py b/google_auth_oauthlib/flow.py
index 7714524..76a8780 100644
--- a/google_auth_oauthlib/flow.py
+++ b/google_auth_oauthlib/flow.py
@@ -160,9 +160,7 @@ def from_client_config(cls, client_config, scopes, **kwargs):
 
         # these args cannot be passed to requests_oauthlib.OAuth2Session
         code_verifier = kwargs.pop("code_verifier", None)
-        autogenerate_code_verifier = kwargs.pop("autogenerate_code_verifier", None)
-        if not code_verifier and autogenerate_code_verifier is None:
-            autogenerate_code_verifier = True
+        autogenerate_code_verifier = kwargs.pop("autogenerate_code_verifier", True)
 
         (
             session,
@@ -239,7 +237,7 @@ def authorization_url(self, **kwargs):
                 specify the ``state`` when constructing the :class:`Flow`.
         """
         kwargs.setdefault("access_type", "offline")
-        if self.autogenerate_code_verifier:
+        if self.code_verifier is None and self.autogenerate_code_verifier:
             chars = ascii_letters + digits + "-._~"
             rnd = SystemRandom()
             random_verifier = [rnd.choice(chars) for _ in range(0, 128)]