GitHub · Pull requests · Forks · Checked October 27, 2026

GitHub: a fork cannot be synced

A branch of a fork is synced with its upstream repository from the Sync fork menu on GitHub, with gh repo sync, or by merging the upstream branch on the command line. When the changes from the upstream repository conflict with the fork branch, GitHub prompts you to create a pull request to resolve the conflicts, and the GitHub CLI cannot sync (GitHub's syncing a fork, checked October 27, 2026).

git fetch upstream
git checkout main
git merge upstream/main
git push origin main

Why it does not sync

On GitHub: Sync fork, above the list of files of the fork, shows the commits from the upstream repository and updates the branch with Update branch. If those changes cause conflicts, GitHub prompts you to create a pull request to resolve them instead.
With the GitHub CLI: gh repo sync OWNER/FORK -b BRANCH-NAME updates the remote fork from its parent. If the changes conflict it cannot sync; to overwrite the destination branch, use --force.
With the REST API: POST /repos/OWNER/REPO/merge-upstream with branch answers 200 with a merge_type of merge, fast-forward or none, 409 when the branch could not be synced because of a merge conflict, and 422 when it could not be synced for some other reason.
Only a local copy: syncing on the command line updates only your local copy of the repository; the fork on GitHub changes once you push.

Syncing on the command line

An upstream remote: before you can sync, configure a remote that points to the upstream repository: git remote add upstream https://github.com/ORIGINAL-OWNER/ORIGINAL-REPOSITORY.git, then check it with git remote -v (GitHub's configuring a remote repository for a fork).
Fetch and merge: git fetch upstream stores the upstream branches as upstream/BRANCH-NAME; check out the fork branch and merge upstream/main into it. Without commits of its own, Git fast-forwards it; with them, you may have to resolve conflicts.
Push: push the merged branch to the fork on GitHub.

What to do

Conflicts on GitHub: create the pull request GitHub offers and resolve the conflicts there, or merge the upstream branch on the command line, resolve the conflicts, and push. See merge conflicts.
Overwriting the fork branch: gh repo sync with --force overwrites the destination branch, so use it only when the fork branch has nothing to keep.
A pull request from the fork: syncing updates a branch of the fork, such as its default branch. A pull request whose branch is behind its base branch is updated from the pull request: see updating the branch.

GitHub pull requests in IntelliJ IDEA

Pull Request Inbox for GitHub, a plugin by Lesstep for JetBrains IDEs 2024.1 or later, shows a pull request's reviews, checks and conversations next to the diff, and merges it with the methods the target branch allows. It checks out a pull request from a fork from the head GitHub keeps for it in the target repository (refs/pull/NUMBER/head), into a local branch named after the pull request, so the fork does not have to be added as a remote; it does not sync forks. The review inbox, diffs and conversations are free; approving, commenting, resolving and merging are Pro (US$1.50 a month, with a 30-day trial).

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