Resolving the "expl3.sty" and Format File Mismatch Error in LaTeX (TeX Live/TinyTeX)

Last updated on May 7, 2025 4 min read Rstudio, R, Python

If you’re encountering the following LaTeX error when compiling a Bookdown or Quarto PDF document:

! LaTeX Error: Mismatched LaTeX support files detected.
(LaTeX)        Loading 'expl3.sty' aborted!
(LaTeX)        The L3 programming layer in the LaTeX format
(LaTeX)        is dated 2025-03-26, but in your TeX tree the files require
(LaTeX)        at least 2025-04-14.

You’re not alone. This issue typically arises from a partial or inconsistent update to your LaTeX distribution — especially with TeX Live or TinyTeX — where the base format files (*.fmt) are out of sync with newer packages like expl3.sty.

This blog post offers a comprehensive, step-by-step fix, especially for Windows users, and documents solutions to every roadblock you may hit — from missing binaries to Perl errors and administrative permissions.

Problem Summary

LaTeX is complaining because the date of the internal format (e.g., latex.fmt) is older than what updated packages expect. This happens when:

  • You run tlmgr update --all, but it doesn’t regenerate format files.
  • You update only parts of TinyTeX or TeX Live.
  • You switch between different LaTeX installations (e.g., TinyTeX + full TeX Live).

Quick Fix Summary

If you’re an expert and want the short answer:

# In Windows Command Prompt (Run as Administrator)
perl C:\texlive\2025\texmf-dist\scripts\texlive\fmtutil.pl --sys --all

But chances are you’ll hit several issues before getting this to work. Read on for the full guide.

Step-by-Step Solution (for Windows + TeX Live 2025)

Step 1: Confirm the Error

In R or Quarto, your error log will say:

Error: LaTeX failed to compile data_analysis.tex. See https://yihui.org/tinytex/r/#debugging

Step 2: Check Version Mismatch

From a terminal:

kpsewhich expl3.sty

Then inspect the header of that file:

%% File: expl3.sty 2025-04-14

If your LaTeX format is older (e.g., 2025-03-26), you have a mismatch.

Step 3: Try Updating TeX Live

tlmgr update --self --all

This updates packages, but does not rebuild the formats. Hence, the problem remains.

Step 4: Rebuild Format Files Manually

This is where most people get stuck.

Try:

fmtutil-sys --all

But you might get this:

'kpsewhich' is not recognized as an internal or external command

Step 5: Fix kpsewhich and PATH Issues

Ensure TeX Live’s binaries are in your PATH:

Add this to your environment variables:

C:\texlive\2025\bin\windows

Then restart your Command Prompt and verify:

where kpsewhich

Should return:

C:\texlive\2025\bin\windows\kpsewhich.exe

Step 6: Use a Valid Perl Interpreter

TeX Live relies on Perl scripts like fmtutil.pl, but many Windows users:

  • Don’t have Perl
  • Have the wrong Perl (e.g., Rtools)

Install Strawberry Perl — use the .msi version.

After installation:

where perl

Ensure it returns:

C:\Strawberry\perl\bin\perl.exe

If it still shows Rtools Perl (C:\rtools44\usr\bin\perl.exe), reorder your system PATH so that Strawberry\perl\bin comes first.

Step 7: Run the Fix

Now you’re ready. In Administrator Command Prompt, run:

set PATH=C:\texlive\2025\bin\windows;%PATH% && perl C:\texlive\2025\texmf-dist\scripts\texlive\fmtutil.pl --sys --all

This rebuilds all format files (57 in total). Success will look like:

[INFO]: successfully rebuilt formats: 54
[INFO]: exiting with status 0

Common Errors and Their Fixes

'kpsewhich' is not recognized

Add C:\texlive\2025\bin\windows to your PATH.

'perl.exe' not recognized

Install Strawberry Perl, not Rtools Perl.

Can't locate Win32/Shortcut.pm

Run:

cpan Win32::Shortcut

Permission denied to create temp directory

Run the command as Administrator.

Final Test

Once the formats are rebuilt, return to R or Quarto:

bookdown::render_book("index.Rmd", "bookdown::pdf_book")

This should now compile without errors.

Notes for TinyTeX Users

If you use tinytex::install_tinytex(), you can also try:

tinytex::reinstall_tinytex()

This wipes and reinstalls TinyTeX, usually resolving the mismatch. However, it may still miss Win32::Shortcut.pm, so you might need to install Strawberry Perl anyway for advanced fixes.

Save Yourself the Trouble Next Time

Create a .bat file with this content:

@echo off
set PATH=C:\texlive\2025\bin\windows;%PATH%
perl C:\texlive\2025\texmf-dist\scripts\texlive\fmtutil.pl --sys --all
pause

Right-click → Run as Administrator whenever you update TeX Live.

Closing Thoughts

This issue is a perfect storm of LaTeX ecosystem complexity:

  • TeX Live doesn’t auto-rebuild format files
  • Windows doesn’t ship Perl
  • tlmgr updates break things if not followed up with fmtutil
  • PATH precedence is fragile

By following the steps above, you ensure your LaTeX system remains consistent and stable — and your academic PDF documents continue compiling smoothly.

Feel free to share this guide or embed it in your internal documentation.

If you have suggestions or spot new errors not covered here, leave a comment!

Mike Nguyen, PhD
Mike Nguyen, PhD
Visiting Professor of Data Sciences and Operations

My research interests include marketing, and social science.

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