10 Most Common LaTeX Compilation Errors and How to Fix Them

You hit compile. Instead of your PDF, you get a wall of red text that looks like it was written by a malfunctioning printer from 1985. An exclamation mark, a cryptic message, a line number that points somewhere unhelpful, and zero indication of what actually went wrong.

If your LaTeX won’t compile and you’re staring at error messages you don’t understand, this guide is for you. We’ve fixed thousands of LaTeX compilation errors across journal papers, conference submissions, and PhD theses. These are the 10 errors we see most often – with the exact error message, what it actually means, and copy-paste code to fix it.

Every error below includes the actual LaTeX error output, a broken code example, and the corrected version. If you’re debugging before a deadline, skip straight to the error that matches your message.

How to Read a LaTeX Error Message

Before diving into specific errors, understanding the anatomy of a LaTeX error message saves hours of debugging. Every LaTeX error follows the same structure:

! Undefined control sequence.
l.42 \begn
{document}

• ! means it’s an error (not a warning). Errors stop compilation.
• The message (“Undefined control sequence”) tells you the category of problem.
• l.42 is the line number where LaTeX detected the error. The actual cause is often on this line or a few lines above.
• The broken command is shown split across the line break. Here, \begn is the culprit – it should be \begin.

Key debugging principle: LaTeX reports where it noticed the error, not necessarily where the error is. A missing brace on line 89 might not trigger an error until line 347. Always look above the reported line if the line itself looks correct.

1. Undefined Control Sequence

What you see: ! Undefined control sequence. l.42 \includegraphics

This is the most common LaTeX error. It means LaTeX encountered a command it does not recognize. The error log tells you the exact line number and the exact command that failed.

The three causes:

Typo in the command name. LaTeX commands are case-sensitive. \textBf{} fails because the correct command is \textbf{}. \Usepackage{} fails because it is \usepackage{}. Check the spelling and capitalization of the command on the line the error points to.

Missing package. Many commands only exist after you load the package that defines them. If you use a command without loading its package, LaTeX does not know what it is. The fix is to add the correct \usepackage{} line to your preamble.

Copy-pasted text from Word or the web. Text pasted from Word, Google Docs, or websites often contains invisible characters that look like backslashes or braces but are different bytes. These produce undefined control sequence errors on lines that look perfectly correct. Delete the line and retype it manually.

The 10 Most Common Triggers

These are the specific commands that produce “undefined control sequence” most often, based on forum questions and support requests we see regularly.

\includegraphics{} without \usepackage{graphicx} in the preamble. This is the single most frequent trigger.

\citep{} or \citet{} without \usepackage{natbib}. These citation commands belong to natbib. If you are using biblatex instead, the equivalents are \parencite{} and \textcite{}.

\href{} or \url{} without \usepackage{hyperref} or \usepackage{url}.

\textcolor{} or \definecolor{} without \usepackage{xcolor} (or the older \usepackage{color}).

\begin{align} without \usepackage{amsmath}. The align environment is not part of base LaTeX.

\boldsymbol{} without \usepackage{amssymb} or \usepackage{amsmath}.

\toprule, \midrule, \bottomrule without \usepackage{booktabs}. These table formatting commands are not built in.

\lstinputlisting{} or \begin{lstlisting} without \usepackage{listings}.

\SI{} or \si{} without \usepackage{siunitx}. Common in physics and engineering papers.

\subfloat{} or \subfigure{} without \usepackage{subfig} or \usepackage{subcaption}. Note that the subfigure package is deprecated — use subcaption instead, which provides \subcaptionbox{} and the subfigure environment.

How to read the error log: The line number in the error message points to where LaTeX stopped, but the actual problem is sometimes on the line above. If the command on the reported line looks correct, check the previous line for a missing closing brace } or an incomplete command that caused LaTeX to misread the next line.
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2. Missing $ Inserted

What you see: ! Missing $ inserted. l.27 The growth rate was 15%

This error means LaTeX found a character that only works inside math mode, but you used it in regular text. LaTeX is telling you it tried to insert a $ to enter math mode because it had no other way to process the character.

The most common triggers:

Underscore _ in regular text. In LaTeX, _ means subscript and only works inside math mode. If you write file_name in text, LaTeX breaks. Fix: file\_name or \texttt{file\_name}. This is especially common inside \includegraphics{} and \bibliography{} paths — \includegraphics{my_figure.pdf} fails because the underscore is interpreted as a subscript command.

Caret ^ in regular text. The caret means superscript in math mode. If you write 2^3 in text expecting it to just display as-is, LaTeX errors. Fix: $2^3$ if you want the superscript, or 2\^{}3 if you want the literal caret character.

Percent % without escaping. LaTeX treats % as a comment character, so 15% makes LaTeX think everything after the % is a comment. The next line then starts in an unexpected state, often producing the “missing $” error. Fix: 15\%.

Ampersand & outside tables. The & character is a column separator in tabular environments. Using it in regular text (like Smith & Sons) causes errors. Fix: Smith \& Sons.

Hash # in text. LaTeX reserves # for macro parameters. Writing issue #42 fails. Fix: issue \#42.

Special Characters Pasted From Word or the Web

If your error appears on a line that looks perfectly correct, the problem is almost certainly an invisible character from copy-paste. Word, Google Docs, and websites insert characters that look identical to their LaTeX equivalents but are different bytes:

Smart quotes (" " instead of " ") cause LaTeX to misinterpret the line. Fix: delete and retype using `` for opening and '' for closing quotes.

The degree symbol (°) pasted from Word triggers math mode errors. Fix: use \textdegree{} from the textcomp package, or $^\circ$.

Em dashes (—) and en dashes (–) pasted as Unicode characters can cause unexpected errors. Fix: delete and retype as --- for em dash and -- for en dash.

The micro sign (µ) and other Unicode symbols from scientific text break pdflatex. Fix: use the appropriate LaTeX command ($\mu$ for micro), or add \usepackage[utf8]{inputenc} to your preamble.

Quick Reference: Special Characters in LaTeX

_ → \_    ^ → \^{}    % → \%    & → \&    # → \#    $ → \$    { → \{    } → \}    ~ → \textasciitilde{}    \ → \textbackslash{}

How to read the error log: The line number points to where LaTeX encountered the unexpected character. If you cannot spot it visually, look for any of the ten special characters listed above without a backslash in front of them. If the line looks clean, delete it entirely and retype it manually to eliminate invisible Unicode characters.

3. Missing } Inserted

What you see: ! Missing } inserted. l.58 \end{document}

This error means LaTeX reached a point where it expected a closing brace } but did not find one. The line number in the error is where LaTeX gave up looking, not where the missing brace should be. The actual problem is almost always earlier in the document.

Why the line number is misleading: If you forget a } on line 30, LaTeX keeps reading, treating everything after line 30 as part of the same argument. It might not realize something is wrong until it hits \end{document} on line 200. The error says line 200, but the fix is on line 30. This is why this error is harder to debug than most.

The most common causes:

Nested commands with one brace dropped. Commands inside commands are where braces go missing most often. \textbf{\textit{some text} is missing the outer closing brace. The more deeply nested your commands, the easier it is to lose track. Fix: count the opening and closing braces on each line. They should match.

Multi-line commands. When a command argument spans multiple lines (like a long \title{} or \caption{}), the closing brace on the last line is easy to accidentally delete during editing. If the error points to a line well after your last edit, look for a multi-line command above that is missing its closing brace.

Runaway argument from a missing brace in environments. A missing } inside a tabular, figure, or equation environment causes LaTeX to consume the \end{...} as part of the argument, which then triggers a cascade of errors. If you see “missing }” followed by “missing \endgroup” or “\end{document} ended by \endgroup”, the root cause is a single missing brace inside an environment earlier in the file.

Macro definitions. Custom commands defined with \newcommand or \def are especially prone to brace mismatches because the definition itself contains braces that are separate from the argument braces. \newcommand{\highlight}[1]{\textbf{\textcolor{red}{#1}} is missing the final } that closes the \newcommand. These errors only appear when you use the command, not when you define it, so the error line points to the usage, not the definition.

How to Find the Missing Brace

Use your editor’s brace matching. In Overleaf, click on any brace and its matching partner highlights. In VS Code with the LaTeX Workshop extension, matching braces are highlighted automatically. In TeXstudio, use Edit, Go to Matching Brace (Ctrl+Shift+B). Place your cursor on each opening brace and check that the highlighted match is where you expect it.

Binary search the document. If the document is long and the error points to \end{document}, comment out the bottom half of your document with % and recompile. If the error disappears, the missing brace is in the bottom half. If it persists, it is in the top half. Keep halving until you find the section that causes it. This takes 4-5 compiles for even a 50-page document.

Look at the line before your last edit. In most cases, the missing brace was introduced by a recent edit. If your document compiled 10 minutes ago and now it does not, the brace you deleted is near whatever you last changed.

Check the log for “Runaway argument.” If the error log says Runaway argument? {some text from your document... before the “missing }” error, LaTeX is showing you the text it consumed while looking for the brace. The beginning of that text is exactly where the missing brace should be.

Error #4: \begin{X} Ended by \end{Y} (Environment Mismatch)

! LaTeX Error: \begin{figure} on input line 45
ended by \end{table}.

What it means: You opened one environment (like \begin{figure}) but closed a different one (\end{table}). This usually happens from copy-paste mistakes or when environments are nested in the wrong order.

❌ Wrong:

\begin{figure}
\begin{center}
\includegraphics{plot.png}
\end{figure} % Should close center first!
\end{center}

✅ Fix:

\begin{figure}
\begin{center}
\includegraphics{plot.png}
\end{center} % Close inner environment first
\end{figure} % Then close outer environment

Environments must nest properly – like matching parentheses. The last environment opened must be the first one closed. This is especially common with figure, center, table, and tabular environments nested together. For a full list of environment types, see the LaTeX Wikibook errors guide.

Error #5: File Not Found

! LaTeX Error: File `results.png' not found.
l.67 \includegraphics{results.png}

What it means: LaTeX can’t find a file you referenced – usually an image (\includegraphics), an input file (\input), or a bibliography (\bibliography). The file either doesn’t exist, is in the wrong folder, or has a different name than what you typed.

✅ Fix – check these in order:

• Is the filename spelled exactly right? LaTeX is case-sensitive on Linux/Overleaf. results.PNG and results.png are different files.
• Is the file in the right folder? If your main.tex is in the root and images are in a figures/ subfolder, use \includegraphics{figures/results.png} or add \graphicspath{{figures/}} to your preamble.
• Did you include the graphicx package? \usepackage{graphicx} must be in your preamble for \includegraphics to work.
• For bibliography files: use \bibliography{references} without the .bib extension. LaTeX adds it automatically.

Pro tip: Avoid spaces and special characters in filenames. Use figure-1.png not Figure 1 (final).png. This prevents path resolution issues across operating systems and Overleaf. You can look up any package and its correct name on the CTAN package archive.

Error #6: Missing \begin{document}

! LaTeX Error: Missing \begin{document}.
l.12 T
his is my introduction

What it means: LaTeX found text content before \begin{document}. Everything before \begin{document} is the preamble, where only declarations (\usepackage, \title, etc.) are allowed. Any actual text, even a stray character, triggers this error.

❌ Common triggers:

documentclass{article}
\usepackage{amsmath}
This is my paper % Text before \begin{document}!
\begin{document}

✅ Fix:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
This is my paper % Text after \begin{document}

This also triggers when a package has a syntax error in its loading, or when you have invisible characters (like BOM markers from Windows text editors) at the start of the file. If you can’t see any stray text, try re-saving the file with UTF-8 encoding (no BOM).

Error #7: Overfull \hbox (Content Too Wide)

Overfull \hbox (15.0pt too wide) in paragraph
at lines 42--45

What it means: This is a warning, not an error – your document will still compile. But it means LaTeX couldn’t fit content within the text margins. The affected line will stick out into the right margin. Common causes: long URLs, wide tables, long inline equations, or unbreakable words.

✅ Fixes (choose based on cause):

% For long URLs:
\usepackage{url}
\url{https://very-long-url.example.com/path}

% For general text overflow:
\usepackage{microtype} % Improves justification globally

% For wide images:
\includegraphics[width=\textwidth]{image}

% For wide tables:
\resizebox{\textwidth}{!}{\begin{tabular}...\end{tabular}}

% Nuclear option for specific paragraphs:
{\sloppy This problematic paragraph with long words.}

While overfull hbox warnings don’t prevent compilation, journals may reject papers with content extending beyond margins. Always check the PDF visually before submission.

Error #8: Undefined Citation [?] and Bibliography Not Showing

LaTeX Warning: Citation `smith2024' on page 3 undefined.
LaTeX Warning: There were undefined references.

What it means: Your \cite{} commands are showing [?] instead of citation numbers, and/or your bibliography is empty. This is the most common BibTeX-related issue and almost always comes down to one of three causes.

Cause 1: You haven’t run BibTeX/Biber.

LaTeX needs multiple compilation passes for citations. The correct sequence is:

pdflatex main.tex % Pass 1: writes .aux with citation keys
bibtex main % Processes .bib and creates .bbl
pdflatex main.tex % Pass 2: reads .bbl
pdflatex main.tex % Pass 3: resolves cross-references

In Overleaf, this happens automatically. If it’s still broken, click the dropdown next to Recompile and select “Recompile from scratch.” For a full walkthrough of bibliography setup, see the Overleaf BibTeX guide.

Cause 2: Citation key mismatch.

BibTeX keys are case-sensitive. If your .bib file has Smith2024 but you write \cite{smith2024}, it won’t match.

Cause 3: BibTeX vs Biber confusion.

If you use \usepackage{biblatex}, the default backend is Biber, not BibTeX. Running bibtex on a biblatex document won’t work. Make sure your editor runs the correct tool.

Error #9: Option Clash or Package Conflict

! LaTeX Error: Option clash for package geometry.
! Package X Error: ... incompatible with package Y.

What it means: You’ve loaded a package twice with different options, or two packages are trying to do the same thing and conflicting.

This is very common when combining a journal template (.cls file) with your own \usepackage declarations – the template may already load a package with specific options.

✅ Fixes:

• Check if the journal template already loads the package. Open the .cls file and search for \RequirePackage or \usepackage. If it loads geometry, don’t load it again in your preamble.
• If you need different options, use \PassOptionsToPackage{options}{package} before \documentclass.
• Load hyperref last. The hyperref package conflicts with many other packages and should almost always be the last \usepackage in your preamble. (See our guide on IEEE LaTeX template formatting for template-specific package loading order.)

Pro tip: When debugging package conflicts, comment out packages one at a time and recompile after each. This isolates which combination is causing the conflict. The Overleaf error docs cover the most common package conflicts in detail.

Error #10: Runaway Argument (Paragraph Ended Before Command Was Complete)

Runaway argument?
! Paragraph ended before \textbf was complete.
l.156

What it means: A command that expects its argument on one line (like \textbf{…}) found a blank line (which LaTeX interprets as a paragraph break) before the closing brace. This usually means a missing } somewhere inside the command’s argument.

❌ Wrong:

\textbf{This is bold text that continues

into the next paragraph without closing the brace.}

✅ Fix:

\textbf{This is bold text that continues
into the next line, with the closing brace on time.}

New paragraph starts here.

If you legitimately need a paragraph break inside a formatted block, use \par instead of a blank line. But usually this error means a brace was simply forgotten.

The 5-Minute LaTeX Debugging Strategy

When your LaTeX document won’t compile and you don’t know where to start, use this systematic approach:

• Read the first error only. Fix error #1 and recompile. One error often cascades into 20+ messages. Fixing the first one frequently eliminates all the others.
• Check the line number. Go to the reported line. If that line looks correct, look 5–10 lines above it. That’s where the actual problem usually is.
• Use binary search for mysterious errors. Comment out half your document. If it compiles, the error is in the commented half. Uncomment half of that and repeat.
• Delete auxiliary files. Delete all .aux, .bbl, .blg, .log, .toc, .lof, .lot files and recompile from scratch. In Overleaf, use “Recompile from scratch” from the dropdown. Corrupted auxiliary files cause phantom errors. If you’re still stuck, TeX Stack Exchange has solutions for virtually every known compilation error.”
• Compile incrementally. Don’t write 20 pages and then compile. Compile after every section, every table, every equation. Finding the error is trivial when you know it’s in the last 10 lines you added.

Quick Reference: All 10 Errors at a Glance

Bookmark this table. When you see an error message, match it to the error type and jump to the fix.

Frequently Asked Questions

Why won’t my LaTeX document compile?

The most common reasons a LaTeX document won’t compile are: undefined control sequences (typos or missing packages), unbalanced braces, math-mode characters in regular text, environment mismatches, and missing files. Read the first error message carefully – it tells you the category of problem. Fix the first error and recompile, since one error often cascades into many.

How do I fix “Undefined control sequence” in LaTeX?

Check three things in order: (1) Is the command spelled correctly? (2) Have you loaded the package that provides the command with \usepackage{packagename}? (3) Are you using the command in the right context – for example, math commands like \alpha need to be inside $ delimiters. If the error points to a line that looks correct, a missing brace above is often the real cause.

How do I fix “Missing $ inserted” in LaTeX?

This error means you used a math-mode character (like _, ^, or a Greek letter command) outside of math mode. Wrap the mathematical expression in $ delimiters for inline math, or use a display math environment like \begin{equation}. If you want to use _ as a literal underscore in text, write \_ instead.

Why are my LaTeX citations showing [?] instead of numbers?Citations show [?] when BibTeX or Biber hasn’t processed your bibliography. Run the full compilation sequence: pdflatex, then bibtex (or biber for biblatex), then pdflatex twice. Also check that your citation keys match exactly between \cite{} and your .bib file – keys are case-sensitive. In Overleaf, try “Recompile from scratch”.

What is “Overfull hbox” and should I fix it?

An overfull hbox warning means some content extends beyond your text margins. It’s a warning, not an error – your document will still compile. However, journals may reject submissions with content overflowing margins. Fix it with \usepackage{microtype} for general text, resize images with width=\textwidth, or break long URLs with the url package.