diff --git a/changelog.d/6702.misc b/changelog.d/6702.misc
new file mode 100644
index 000000000000..f7bc98409c80
--- /dev/null
+++ b/changelog.d/6702.misc
@@ -0,0 +1 @@
+Remove duplicate check for the `session` query parameter on the `/auth/xxx/fallback/web` Client-Server endpoint.
\ No newline at end of file
diff --git a/synapse/rest/client/v2_alpha/auth.py b/synapse/rest/client/v2_alpha/auth.py
index 7a256b6ecb13..50e080673b3b 100644
--- a/synapse/rest/client/v2_alpha/auth.py
+++ b/synapse/rest/client/v2_alpha/auth.py
@@ -206,10 +206,6 @@ async def on_POST(self, request, stagetype):
 
             return None
         elif stagetype == LoginType.TERMS:
-            if ("session" not in request.args or len(request.args["session"])) == 0:
-                raise SynapseError(400, "No session supplied")
-
-            session = request.args["session"][0]
             authdict = {"session": session}
 
             success = await self.auth_handler.add_oob_auth(