diff --git a/synapse/http/server.py b/synapse/http/server.py
index ce9d5630df2..e87842f0c7e 100644
--- a/synapse/http/server.py
+++ b/synapse/http/server.py
@@ -973,6 +973,11 @@ def set_cors_headers(request: "SynapseRequest") -> None:
     request.setHeader(
         b"Access-Control-Allow-Methods", b"GET, HEAD, POST, PUT, DELETE, OPTIONS"
     )
+
+    # Allow browsers to cache preflight responses for 10 minutes
+    if request.method == b"OPTIONS":
+        request.setHeader(b"Access-Control-Max-Age", b"600")
+
     if request.path is not None and (
         request.path == b"/_matrix/client/unstable/org.matrix.msc4108/rendezvous"
         or request.path.startswith(b"/_synapse/client/rendezvous")