I am re-compiling a document I haven't compiled in a while.

I updated all the packages and I am getting this error message:

! LaTeX Error: Mismatched LaTeX support files detected.
Loading 'l3backend-pdftex.def' aborted!

The L3 programming layer in the LaTeX format
is dated 2020-09-03, but in your TeX tree the files require
at least 2021-02-18.

the "l3backend" package is installed and up-to-date. I have tried uninstalling it and reinstalling it. I have located the files and on line 29 I find:


so it should fulfil the requirement (as far as I understand).

I have read this question, but if possible I'd like not to switch out of MiKTeX.

Is there a way to solve this issue?

  • texworks is just your editor and does not load the file at all, make sure you updated miktex in both user and admin mode Nov 14, 2022 at 13:57
  • 1
    What does kpsewhich --all -engine=pdftex pdflatex.fmt report? Nov 14, 2022 at 13:58
  • @UlrikeFischer "major issue: user/administrator updates are out-of-sync" uuuuh.... how do I fix this?
    – Federico
    Nov 14, 2022 at 14:00
  • as David wrote: check for update in user and admin mode. Nov 14, 2022 at 14:03
  • Update miktex in both miktex user and miktex admin mode.
    – daleif
    Nov 14, 2022 at 14:03

1 Answer 1


If you installed miktex in multi-user mode ("for all users") it typically has a texmf tree for all users and a texmf tree for every user account which contains packages that this user installs "only for me" (e.g. through the on-the-fly option). It is then important that you maintain miktex in admin mode ("for all users") and user mode ("for you only") to avoid that the two trees get out of sync.

So always check for updates in both modes.


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