starlette RuntimeError: Got invalid message type on

The Fix

Upgrade to version 0.13.4 or later.

Based on closed Kludex/starlette issue #330 · PR/commit linked

Production note: Most teams hit this during upgrades or environment changes. Roll out with a canary and smoke critical endpoints (health, OpenAPI/docs) before 100%.

Jump to Verify Open PR/Commit

@@ -100,6 +100,7 @@ from starlette.responses import PlainTextResponse
 class App:
     def __init__(self, scope):
+        assert scope['type'] == 'http'
         self.scope = scope

repro.py

from starlette.responses import PlainTextResponse


class App:
    def __init__(self, scope):
        self.scope = scope

    async def __call__(self, receive, send):
        response = PlainTextResponse('Hello, world!')
        await response(receive, send)

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

fix.md

Option A — Upgrade to fixed release\nUpgrade to version 0.13.4 or later.\nWhen NOT to use: This fix is not applicable if the application needs to handle lifespan messages.\n\n

Why This Fix Works in Production

Trigger: ERROR: Exception in 'lifespan' protocol
Mechanism: The ASGI app did not assert that the scope type was 'http', causing runtime errors
Why the fix works: The example ASGI apps now ensure that the scope['type'] is the expected type, preventing runtime errors related to lifespan messages. (first fixed release: 0.13.4).

Production impact:

If left unfixed, the same config can fail only in production (env differences), causing startup failures or partial feature outages.

Why This Breaks in Prod

Shows up under Python 3.7 in real deployments (not just unit tests).
The ASGI app did not assert that the scope type was 'http', causing runtime errors
Surfaces as: INFO: Started server process [18742]

Proof / Evidence

GitHub issue: #330
Fix PR: https://github.com/kludex/starlette/pull/348
First fixed release: 0.13.4
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.48

Verified Execution

We executed the runnable minimal repro in a temporary environment and captured exit codes + logs.

Status: PASS
Ran: 2026-02-11T16:52:29Z
Package: starlette
Fixed: 0.13.4
Mode: fixed_only
Outcome: ok

Logs

affected (exit=None)

fixed (exit=0)

Discussion

High-signal excerpts from the issue thread (symptoms, repros, edge-cases).

Jump to Sources Open on GitHub

“Labelling this up as a bug, although it's a documentation bug rather than an implementation issue.”

@lovelydinosaur · 2019-01-21 · source

“We should probably change the example to..”

@lovelydinosaur · 2019-01-21 · source

Failure Signature (Search String)

ERROR: Exception in 'lifespan' protocol

Error Message

Stack trace

error.txt

Error Message
-------------
INFO: Started server process [18742]
INFO: Waiting for application startup.
ERROR: Exception in 'lifespan' protocol
Traceback (most recent call last):
  File "/home/matthew/.virtualenvs/dummy/lib/python3.7/site-packages/uvicorn/lifespan.py", line 29, in run
    await self.asgi(self.receive, self.send)
  File "./app.py", line 10, in __call__
    await response(receive, send)
  File "/home/matthew/.virtualenvs/dummy/lib/python3.7/site-packages/starlette/responses.py", line 124, in __call__
    "headers": self.raw_headers,
  File "/home/matthew/.virtualenvs/dummy/lib/python3.7/site-packages/uvicorn/lifespan.py", line 50, in send
    raise RuntimeError(error % message['type'])
RuntimeError: Got invalid message type on lifespan protocol "http.response.start"
ERROR: Application startup failed. Exiting.

Minimal Reproduction

repro.py

from starlette.responses import PlainTextResponse


class App:
    def __init__(self, scope):
        self.scope = scope

    async def __call__(self, receive, send):
        response = PlainTextResponse('Hello, world!')
        await response(receive, send)

Environment

Python: 3.7

What Broke

Application startup failed with a runtime error, preventing the server from running.

Why It Broke

The ASGI app did not assert that the scope type was 'http', causing runtime errors

Fix Options (Details)

Option A — Upgrade to fixed release Safe default (recommended)

Upgrade to version 0.13.4 or later.

When NOT to use: This fix is not applicable if the application needs to handle lifespan messages.

Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.

Fix reference: https://github.com/kludex/starlette/pull/348

First fixed release: 0.13.4

Last verified: 2026-02-09. Validate in your environment.

When NOT to Use This Fix

This fix is not applicable if the application needs to handle lifespan messages.

Verify Fix

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

Did This Fix Work in Your Case?

Quick signal helps us prioritize which fixes to verify and improve.

Prevention

Capture the exact failing error string in logs and tests so you can reproduce via a minimal script.
Pin production dependencies and upgrade only with a reproducible test that hits the failing path.

Version Compatibility Table

Version	Status
0.13.4	Fixed

Related Issues

No related fixes found.

Cluster: starlette:configuration-error All hubs All clusters

Related clusters: Data consistency SSL handshake Other

Sources

We don’t republish the full GitHub discussion text. Use the links above for context.

starlette RuntimeError: Got invalid message type on lifespan protocol "http.response.start" (Fix)