Merge branches with unrelated histories in Git

David Y.

—July 15, 2023

The ProblemThe Problem

During a Git merge, I encounter the following error message:

fatal: refusing to merge unrelated histories
Error redoing merge

How can I fix this error and complete the merge?

The SolutionThe Solution

Git is very flexible and allows us to do things that may not be intuitive for a source control program, such as creating branches in the same repository that have entirely different contents and commit histories. This has some practical uses, such as the gh-pages branch used to publish websites on GitHub Pages.

However, if we attempt to merge two branches without a common base commit, we will encounter this error, which was introduced in Git 2.9.0 to prevent accidental merges of this type, as they are quite unusual.

If this error occurs during a merge that is not intended to combine two separate codebases, there may be a problem with our local Git repository. Reclone the remote version of the repository in a different directory and migrate any local changes there before attempting the merge again.

If we are attempting to combine two separate codebases, we must pass the flag --allow-unrelated-histories to git merge:

git merge --allow-unrelated-histories