diff --git a/orthocal/asgi.py b/orthocal/asgi.py
index e5c1238..060ebf5 100644
--- a/orthocal/asgi.py
+++ b/orthocal/asgi.py
@@ -13,6 +13,7 @@
 
 from django.conf import settings
 from django.core.asgi import get_asgi_application
+from mcp.server.transport_security import TransportSecuritySettings
 
 django_application = get_asgi_application()
 
@@ -24,7 +25,19 @@
 # owns its own /mcp route and lifespan (which starts/stops its session
 # manager's background task). Django's ASGIHandler doesn't implement the
 # lifespan protocol at all, so lifespan scope is only ever handled here.
-mcp_application = mcp.streamable_http_app()
+#
+# transport_security must be set explicitly: with no host argument, the SDK
+# defaults host to '127.0.0.1' and auto-enables DNS-rebinding protection
+# restricted to localhost -- fine in local dev, but it rejects every real
+# request in production (Cloud Run's own hostname as the Host header,
+# forwarded by the Firebase Hosting proxy in front of it, isn't on that
+# allowlist). DNS-rebinding protection defends a server bound to localhost
+# against a malicious webpage's JS reaching it through the browser; it
+# doesn't apply to a public HTTPS API with no localhost-only trust boundary,
+# so disabling it here is the correct fix, not a workaround.
+mcp_application = mcp.streamable_http_app(
+    transport_security=TransportSecuritySettings(enable_dns_rebinding_protection=False),
+)
 
 
 async def application(scope, receive, send):