diff --git a/authlib/oauth2/rfc6749/parameters.py b/authlib/oauth2/rfc6749/parameters.py
index 4ffdb1d6..8c3a5aa6 100644
--- a/authlib/oauth2/rfc6749/parameters.py
+++ b/authlib/oauth2/rfc6749/parameters.py
@@ -60,7 +60,7 @@ def prepare_grant_uri(uri, client_id, response_type, redirect_uri=None,
         params.append(('state', state))
 
     for k in kwargs:
-        if kwargs[k]:
+        if kwargs[k] is not None:
             params.append((to_unicode(k), kwargs[k]))
 
     return add_params_to_uri(uri, params)
diff --git a/tests/core/test_oauth2/test_rfc6749_misc.py b/tests/core/test_oauth2/test_rfc6749_misc.py
index 612353bd..22ee8f2b 100644
--- a/tests/core/test_oauth2/test_rfc6749_misc.py
+++ b/tests/core/test_oauth2/test_rfc6749_misc.py
@@ -50,6 +50,13 @@ def test_parse_implicit_response(self):
             rv,
             {'access_token': 'a', 'token_type': 'bearer', 'state': 'c'}
         )
+    
+    def test_prepare_grant_uri(self):
+        grant_uri = parameters.prepare_grant_uri('https://i.b/authorize', 'dev', 'code', max_age=0)
+        self.assertEqual(
+            grant_uri,
+            "https://i.b/authorize?response_type=code&client_id=dev&max_age=0"
+        )
 
 
 class OAuth2UtilTest(unittest.TestCase):