The Fix
Upgrade to version 0.13.4 or later.
Based on closed Kludex/starlette issue #327 · 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%.
@@ -1,9 +1,11 @@
@@ -1,9 +1,11 @@
+import tempfile
import typing
from collections import namedtuple
4.3. Multiple Files for One Form Field
The form data for a form field might include multiple files.
[RFC2388] suggested that multiple files for a single form field be
transmitted using a nested "multipart/mixed" part. This usage is
deprecated.
To match widely deployed implementations, multiple files MUST be sent
by supplying each file in a separate part but all with the same
"name" parameter.
Receiving applications intended for wide applicability (e.g.,
multipart/form-data parsing libraries) SHOULD also support the older
method of supplying multiple files.
Re-run the minimal reproduction on your broken version, then apply the fix and re-run.
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 does not require handling multiple files for a single field.\n\n
Why This Fix Works in Production
- Trigger: Support for Multiple Files for One Form Field
- Mechanism: The form data structure did not support multiple files for a single form field as per RFC 7578
- Why the fix works: Adds support for handling multiple files for a single form field in the form data structure. (first fixed release: 0.13.4).
- 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
- The form data structure did not support multiple files for a single form field as per RFC 7578
Proof / Evidence
- GitHub issue: #327
- Fix PR: https://github.com/kludex/starlette/pull/339
- 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: 0.57
Discussion
High-signal excerpts from the issue thread (symptoms, repros, edge-cases).
“Absolutely yes. Have this on the backlog here https://github.com/encode/starlette/issues/114 but I’ll try to bump up the priority, unless someone gets to it before me.”
“I think the QueryParams data structure has all the functionality we need, tho we’ll want to do some renaming.”
“I saw that issue but wasn't sure if it was the same thing”
Failure Signature (Search String)
- Support for Multiple Files for One Form Field
Error Message
Signature-only (no traceback captured)
Error Message
-------------
Support for Multiple Files for One Form Field
Minimal Reproduction
4.3. Multiple Files for One Form Field
The form data for a form field might include multiple files.
[RFC2388] suggested that multiple files for a single form field be
transmitted using a nested "multipart/mixed" part. This usage is
deprecated.
To match widely deployed implementations, multiple files MUST be sent
by supplying each file in a separate part but all with the same
"name" parameter.
Receiving applications intended for wide applicability (e.g.,
multipart/form-data parsing libraries) SHOULD also support the older
method of supplying multiple files.
Why It Broke
The form data structure did not support multiple files for a single form field as per RFC 7578
Fix Options (Details)
Option A — Upgrade to fixed release Safe default (recommended)
Upgrade to version 0.13.4 or later.
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/339
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 does not require handling multiple files for a single field.
Verify Fix
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.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.