diff --git a/changelog.d/11451.bugfix b/changelog.d/11451.bugfix
new file mode 100644
index 000000000000..960714d0f9a4
--- /dev/null
+++ b/changelog.d/11451.bugfix
@@ -0,0 +1 @@
+Add support for the `/_matrix/client/v3/login/sso/redirect/{idpId}` API from Matrix v1.1. This endpoint was overlooked when support for v3 endpoints was added in v1.48.0rc1.
diff --git a/synapse/rest/client/login.py b/synapse/rest/client/login.py
index 09f378f91967..a66ee4fb3d4e 100644
--- a/synapse/rest/client/login.py
+++ b/synapse/rest/client/login.py
@@ -513,7 +513,7 @@ class SsoRedirectServlet(RestServlet):
         re.compile(
             "^"
             + CLIENT_API_PREFIX
-            + "/r0/login/sso/redirect/(?P<idp_id>[A-Za-z0-9_.~-]+)$"
+            + "/(r0|v3)/login/sso/redirect/(?P<idp_id>[A-Za-z0-9_.~-]+)$"
         )
     ]
 
diff --git a/synapse/rest/client/room.py b/synapse/rest/client/room.py
index 73d0f7c95002..99f303c88e34 100644
--- a/synapse/rest/client/room.py
+++ b/synapse/rest/client/room.py
@@ -1138,12 +1138,12 @@ async def on_POST(
 
 
 class RoomHierarchyRestServlet(RestServlet):
-    PATTERNS = [
+    PATTERNS = (
         re.compile(
             "^/_matrix/client/(v1|unstable/org.matrix.msc2946)"
             "/rooms/(?P<room_id>[^/]*)/hierarchy$"
         ),
-    ]
+    )
 
     def __init__(self, hs: "HomeServer"):
         super().__init__()