diff --git a/scripts/install-lefthook.spec.ts b/scripts/install-lefthook.spec.ts
index 6a95b2861a..bb6ab4ec16 100644
--- a/scripts/install-lefthook.spec.ts
+++ b/scripts/install-lefthook.spec.ts
@@ -55,6 +55,24 @@ function git(fixture: Fixture, cwd: string, args: string[]): string {
   return result.stdout.trim()
 }
 
+/** Remove the line terminator Git appends to a printed path, as the installer does. */
+function stripGitLineTerminator(output: string): string {
+  const withoutLineFeed = output.endsWith('\n') ? output.slice(0, -1) : output
+  return process.platform === 'win32' && withoutLineFeed.endsWith('\r')
+    ? withoutLineFeed.slice(0, -1)
+    : withoutLineFeed
+}
+
+// `git()` trims, which also drops a worktree directory's own trailing whitespace. Paths that must
+// equal the installer's own reading keep only the line terminator, so a trailing space survives.
+function gitPath(fixture: Fixture, cwd: string, args: string[]): string {
+  const result = gitResult(fixture, cwd, args)
+  if (result.status !== 0) {
+    throw new Error(`git ${args.join(' ')} failed: ${result.stderr}`)
+  }
+  return stripGitLineTerminator(result.stdout)
+}
+
 function write(path: string, content: string, mode?: number): void {
   mkdirSync(dirname(path), { recursive: true })
   writeFileSync(path, content, mode === undefined ? undefined : { mode })
@@ -161,12 +179,12 @@ function gitDirectory(fixture: Fixture, root: string): string {
 // The installer resolves the common directory against Git's own top-level path, and the host
 // spells that path differently from the fixture directory this file created: Git canonicalizes
 // Windows 8.3 short names and the macOS `/var` symlink, while `mkdtempSync` returns the temp
-// directory's own spelling. Resolving the relative common directory against Git's top-level
-// instead of the fixture directory gives the same string the installer computes, so an injected
-// failure on this path reaches the installer's own lock instead of missing it.
+// directory's own spelling. Reading both values the way the installer reads them (`gitPath`, not
+// the trimming `git()`) keeps the relative common directory resolved to the same string the
+// installer computes, so an injected failure on this path reaches the installer's own lock.
 function commonDirectory(fixture: Fixture): string {
-  const root = git(fixture, fixture.main, ['rev-parse', '--show-toplevel'])
-  const output = git(fixture, fixture.main, ['rev-parse', '--git-common-dir'])
+  const root = gitPath(fixture, fixture.main, ['rev-parse', '--show-toplevel'])
+  const output = gitPath(fixture, fixture.main, ['rev-parse', '--git-common-dir'])
   return isAbsolute(output) ? output : resolve(root, output)
 }
 
@@ -397,6 +415,15 @@ syncBuiltinESMExports()
     await expectInjectedLockAccessFailure(fixture, { operation: 'openSync', code: 'EPERM', expires: false })
   })
 
+  // A worktree directory can end in a space on POSIX hosts; Git prints that path verbatim while a
+  // trimming read would drop the space and name a different directory, so the injection only fires
+  // when the expected path is read the installer's way. Windows cannot create such a directory.
+  it.skipIf(process.platform === 'win32')('handles an injected lock failure in a worktree whose path ends with a space', async () => {
+    await expectInjectedLockAccessFailure(createFixture({ main: 'main ' }), {
+      operation: 'openSync', code: 'EPERM', expires: false,
+    })
+  })
+
   it('waits for a concurrent installer to finish publishing its lock record', async () => {
     const fixture = createFixture()
     const lockPath = installLockPath(fixture)