How to Fix “You Can’t Use a Prefix with `\begingroup`” in LaTeX

The error “You can’t use a prefix with \begingroup” means TeX read a prefix command where it expected a definition or assignment, but instead encountered the command that starts a group. The prefix is often \global, though other prefixes can cause the same kind of error.

The cause is usually a misplaced command in your document or in a macro that your document calls. The babel, multicol, and expl3 packages may appear near the failing code, but their presence alone does not identify the cause. First inspect the command immediately before the group begins.

What TeX means by a prefix

A TeX prefix modifies the operation that follows it. For example, \global makes a suitable assignment apply beyond the current group, while \long and \protected modify definitions. These are valid patterns:

\global\def\mycommand{Hello}
\long\def\mycommand#1{#1}

By contrast, \begingroup starts a group; it is not an assignment for a prefix to modify. So this is invalid:

\global\begingroup

The error can also arise when a macro expands to \begingroup before TeX reaches another non-expandable operation. For example:

\def\startgroup{\begingroup}
\global\startgroup % Incorrect: expands to \begingroup while the prefix is pending

LaTeX’s \begin{...} starts an environment and opens a group as part of that process. Putting \global directly before it is not a way to make the environment global. However, \begin has internal operations before the group opens, so \global\begin{...} is not a reliable example of this specific error: the prefix may affect an internal operation or produce a different error. Start the environment normally.

A working multicol example

Start the environment normally. If you need an assignment made inside a group to persist after the group ends, apply \global to that assignment—not to the environment command.

\documentclass{report}
\usepackage[english]{babel}
\usepackage{multicol}

\begin{document}

\begin{multicols}{2}
This text is in the first column. The second column is filled
when the first one is full.
\end{multicols}

\end{document}

This example uses \begin{multicols}{2} without a prefix, which is the normal form. In ordinary document content, you usually do not need to make assignments global. If you do need a global definition, apply the prefix to the definition itself, as in \global\def\name{value}. Prefer LaTeX-level commands such as \newcommand for ordinary document definitions; use low-level global assignments only when you understand the surrounding grouping.

How to locate the offending command

TeX may report the error on a line after the actual mistake, especially when a macro or package command expands into the group-opening command. Use this checklist:

1. Read the error context. Look at the line TeX marks and the lines immediately before it. Find any prefix such as \global, \long, or \protected.
2. Check what the prefix reaches. If it reaches \begingroup, or a macro whose expansion reaches \begingroup before another non-expandable operation, the prefix is likely in the wrong place. An environment command such as \begin{...} is not by itself proof that this is the problem.
3. Inspect macro definitions. If the marked source line looks valid, check any custom command used there. A definition may expand to a group opener after a prefix has been read.
4. Reduce the document. Temporarily remove unrelated packages and content, then add them back until the error returns. This can show whether the issue is in your code or a specific interaction.

For more expansion detail, add \errorcontextlines=999 near the start of the document while debugging. This can make TeX print more of the macro context around an error. Remove the setting once you have finished investigating.

Common mistakes

• Putting \global before an environment. \global\begin{...} does not make the environment global. Start the environment normally and globalize only a suitable assignment inside it, if needed.
• Assuming the reported line is the source of the problem. A macro can expand before TeX detects the invalid prefix, so inspect nearby commands and definitions too.
• Blaming a package from its name or location. A package may expose the problematic code path without containing the mistake. Make a small test document before changing package options or editing package files.
• Adding a prefix to fix a local-scope issue without checking the assignment. A prefix works only when it precedes an operation that supports it. If you only need a value outside a group, consider whether a different LaTeX structure or command is more appropriate.

If the error persists in a small document, include that minimal example and the full error context when asking for help. Those details make it possible to identify which command is actually being prefixed.