diff --git a/lib/rules/line-length.js b/lib/rules/line-length.js
index 2d5b60c..3a568a9 100644
--- a/lib/rules/line-length.js
+++ b/lib/rules/line-length.js
@@ -29,10 +29,14 @@ export default {
     let failed = false
     for (let i = 0; i < parsed.body.length; i++) {
       const line = parsed.body[i]
+
       // Skip quoted lines, e.g. for original commit messages of V8 backports.
       if (line.startsWith('    ')) { continue }
       // Skip lines with URLs.
       if (/https?:\/\//.test(line)) { continue }
+      // Skip co-authorship.
+      if (/^co-authored-by:/i.test(line)) { continue }
+
       if (line.length > len) {
         failed = true
         context.report({
diff --git a/test/rules/line-length.js b/test/rules/line-length.js
index d8bda5f..1de6420 100644
--- a/test/rules/line-length.js
+++ b/test/rules/line-length.js
@@ -129,5 +129,60 @@ https://${'very-'.repeat(80)}-long-url.org/
     tt.end()
   })
 
+  t.test('Co-author lines', (tt) => {
+    const sha = 'f1496de5a7d5474e39eafaafe6f79befe5883a5b'
+    const author = {
+      name: 'Jacob Smith',
+      email: '3012099+JakobJingleheimer@users.noreply.github.com',
+      date: '2025-12-22T09:40:42Z'
+    }
+
+    const v = new Validator()
+    const overlongMessage = `fixup!: apply case-insensitive suggestion
+      Co-authored-by: Michaël Zasso <37011812+targos@users.noreply.github.com>`
+    const bad = new Commit({
+      sha,
+      author,
+      message: overlongMessage
+    }, v)
+
+    bad.report = (opts) => {
+      tt.pass('called report')
+      tt.equal(opts.id, 'line-length', 'id')
+      tt.equal(opts.string, overlongMessage.split('\n')[1], 'string')
+      tt.equal(opts.level, 'fail', 'level')
+    }
+
+    Rule.validate(bad, {
+      options: {
+        length: 72
+      }
+    })
+
+    const good = new Commit({
+      sha,
+      author,
+      message: [
+        'fixup!: apply case-insensitive suggestion',
+        'Co-authored-by: Michaël Zasso <37011812+targos@users.noreply.github.com>'
+      ].join('\n')
+    }, v)
+
+    good.report = (opts) => {
+      tt.pass('called report')
+      tt.equal(opts.id, 'line-length', 'id')
+      tt.equal(opts.string, '', 'string')
+      tt.equal(opts.level, 'pass', 'level')
+    }
+
+    Rule.validate(good, {
+      options: {
+        length: 72
+      }
+    })
+
+    tt.end()
+  })
+
   t.end()
 })