---
license: mit
tags:
  - fastapi
  - python-3.13
  - bcrypt
  - passlib
  - jwt-authentication
---

# 🛡️ Fixing `ValueError: password cannot be longer than 72 bytes` in Python 3.12 / 3.13 (`passlib` + `bcrypt`)

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When deploying **FastAPI** authentication routes using `passlib[bcrypt]` on **Python 3.12 or Python 3.13**, newer versions of `bcrypt` (`>= 4.1.0`) raise:
```text
ValueError: password cannot be longer than 72 bytes, truncate manually if necessary
```
during `passlib`'s internal `detect_wrap_bug` startup check.

## ✅ The Instant Production Fix

Pin `bcrypt==4.0.1` alongside `passlib[bcrypt]` in your `requirements.txt`:

```txt
fastapi
uvicorn
passlib[bcrypt]
bcrypt==4.0.1
python-jose[cryptography]
pydantic[email]
```

---

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