diff --git a/src/git.ts b/src/git.ts
index 90b2fef..8190e0d 100644
--- a/src/git.ts
+++ b/src/git.ts
@@ -131,6 +131,6 @@ export async function hasNewCommits(worktreePath: string): Promise<boolean> {
 /** Detect the main branch name (main or master). */
 export async function mainBranch(cwd?: string): Promise<string> {
   const dir = cwd ?? "."
-  const result = await $`git rev-parse --verify --quiet refs/heads/main`.cwd(dir).nothrow().quiet()
+  const result = await $`git -C ${dir} rev-parse --verify --quiet refs/heads/main`.nothrow().quiet()
   return result.exitCode === 0 ? "main" : "master"
 }