Port, board and/or hardware

unix port, standard variant, x86_64 linux

MicroPython version

v1.27.0-preview-42-gb7cfafc1ee

Reproduction

1. Start micropython interactively
2. enter the following lines one by one at the ">>>" prompt:

import micropython
micropython.heap_lock()

3. press ctrl-d to exit the interactive session

Expected behaviour

No FATAL error

Observed behaviour

This fatal error occurs:

FATAL: uncaught NLR 0x558779c53558

(the address of course varies)

Additional Information

The whole session looks like this:

 ./build-standard/micropython 
MicroPython v1.27.0-preview.42.gb7cfafc1ee.dirty on 2025-08-15; linux [GCC 14.2.0] version
Use Ctrl-D to exit, Ctrl-E for paste mode
>>> import micropython
>>> micropython.heap_lock()
>>> 
FATAL: uncaught NLR 0x55b472d86558

I suppose that this is mostly a "doctor, doctor" situation but it was previously reported in #4205 and was supposed to have been fixed.

Code of Conduct

Yes, I agree