diff --git a/src/cli.js b/src/cli.js
index addb70a..c1888d7 100755
--- a/src/cli.js
+++ b/src/cli.js
@@ -467,8 +467,6 @@ repo
       if (!config || !config.url || !config.token) {
         throw new Error('Not authenticated. Run: stoke auth login');
       }
-      if (!options.branch) throw new Error('--branch is required');
-
       const base = config.url.replace(/\/+$/, '');
       const forgeUrl = `${base}/${encodeURIComponent(options.owner)}/${encodeURIComponent(options.repo)}.git`;
       const result = syncRepository({
@@ -477,7 +475,11 @@ repo
         branch: options.branch,
         env: gitAuthEnv({ ...config, url: base }),
       });
-      console.log(`${result.branch} ${result.oldSha}..${result.newSha}`);
+      if (result.changed) {
+        console.log(`${result.branch} ${result.oldSha}..${result.newSha}`);
+      } else {
+        console.log(`${result.branch} is up to date at ${result.newSha}`);
+      }
     } catch (err) {
       console.error(`Repository sync failed: ${err.message}`);
       process.exit(1);
diff --git a/src/repo-sync.js b/src/repo-sync.js
index 43b5132..3b45379 100644
--- a/src/repo-sync.js
+++ b/src/repo-sync.js
@@ -19,6 +19,15 @@ function syncRepository({ forgeUrl, upstreamUrl, branch, env }) {
 
   try {
     runGit(['init', '--bare', directory], { cwd: directory, env });
+    if (!branch) {
+      const symbolicHead = runGit(['ls-remote', '--symref', forgeUrl, 'HEAD'], {
+        cwd: directory,
+        env,
+      }).stdout;
+      const match = symbolicHead.match(/^ref:\s+refs\/heads\/(.+)\s+HEAD$/m);
+      if (!match) throw new Error('Could not resolve the forge repository default branch');
+      branch = match[1];
+    }
     runGit(['fetch', '--no-tags', forgeUrl, `refs/heads/${branch}:${forgeRef}`], {
       cwd: directory,
       env,
@@ -45,7 +54,7 @@ function syncRepository({ forgeUrl, upstreamUrl, branch, env }) {
         env,
       });
     }
-    return { branch, oldSha, newSha };
+    return { branch, oldSha, newSha, changed: oldSha !== newSha };
   } finally {
     fs.rmSync(directory, { recursive: true, force: true });
   }
diff --git a/test/sync.test.js b/test/sync.test.js
index 4ef49c1..fd72c2c 100644
--- a/test/sync.test.js
+++ b/test/sync.test.js
@@ -55,17 +55,18 @@ function fixture() {
   };
 }
 
-function runSync(fx, extra = []) {
-  return spawnSync(process.execPath, [
+function runSync(fx, extra = [], { branch = 'main' } = {}) {
+  const args = [
     CLI,
     'repo',
     'sync',
     '-o', 'o',
     '-r', 'r',
     '--from', `file://${fx.upstreamRepo}`,
-    '--branch', 'main',
-    ...extra,
-  ], {
+  ];
+  if (branch) args.push('--branch', branch);
+  args.push(...extra);
+  return spawnSync(process.execPath, args, {
     encoding: 'utf8',
     env: { ...process.env, STOKE_CONFIG_FILE: fx.config },
   });
@@ -83,3 +84,30 @@ test('repo sync fast-forwards an undiverged forge branch', () => {
     fx.cleanup();
   }
 });
+
+test('repo sync resolves an omitted branch from the forge symbolic HEAD', () => {
+  const fx = fixture();
+  try {
+    const result = runSync(fx, [], { branch: null });
+
+    assert.equal(result.status, 0, result.stderr);
+    assert.equal(git(['rev-parse', 'refs/heads/main'], fx.forgeRepo), fx.newSha);
+    assert.match(result.stdout, new RegExp(`main ${fx.oldSha}\\.\\.${fx.newSha}`));
+  } finally {
+    fx.cleanup();
+  }
+});
+
+test('repo sync reports an already-current branch as a no-op', () => {
+  const fx = fixture();
+  try {
+    assert.equal(runSync(fx).status, 0);
+    const result = runSync(fx);
+
+    assert.equal(result.status, 0, result.stderr);
+    assert.equal(git(['rev-parse', 'refs/heads/main'], fx.forgeRepo), fx.newSha);
+    assert.match(result.stdout, new RegExp(`main is up to date at ${fx.newSha}`));
+  } finally {
+    fx.cleanup();
+  }
+});