diff --git a/pyproject.toml b/pyproject.toml
index 8388d4f..dc4f67a 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -39,7 +39,7 @@ dependencies = [
 
 [project.optional-dependencies]
 devel = [
-    "httpx",
+    "httpx >= 0.20.0",
 ]
 
 [project.urls]
diff --git a/tests/test_auth.py b/tests/test_auth.py
index f5c1491..bfa7290 100644
--- a/tests/test_auth.py
+++ b/tests/test_auth.py
@@ -66,7 +66,8 @@ class AuthenticationTestCase(unittest.TestCase):
             "DIGEST_AUTH_REALM": REALM,
         })
         self.__client: httpx.Client = httpx.Client(
-            app=app, base_url="https://testserver")
+            transport=httpx.WSGITransport(app=app),
+            base_url="https://testserver")
         """The testing client."""
 
         auth: DigestAuth = DigestAuth()
diff --git a/tests/test_flask_login.py b/tests/test_flask_login.py
index 0a88507..bcf30ea 100644
--- a/tests/test_flask_login.py
+++ b/tests/test_flask_login.py
@@ -91,7 +91,8 @@ class FlaskLoginTestCase(unittest.TestCase):
             "DIGEST_AUTH_REALM": REALM,
         })
         self.__client: httpx.Client = httpx.Client(
-            app=self.app, base_url="https://testserver")
+            transport=httpx.WSGITransport(app=self.app),
+            base_url="https://testserver")
         """The testing client."""
 
         self.__has_flask_login: bool = True