diff --git a/project.py b/project.py
index 48ab847..06240b7 100644
--- a/project.py
+++ b/project.py
@@ -748,16 +748,31 @@
   def StartBranch(self, name):
     """Create a new branch off the manifest's revision.
     """
-    branch = self.GetBranch(name)
-    branch.remote = self.GetRemote(self.remote.name)
-    branch.merge = self.revision
+    try:
+      self.bare_git.rev_parse(R_HEADS + name)
+      exists = True
+    except GitError:
+      exists = False;
 
-    rev = branch.LocalMerge
-    cmd = ['checkout', '-b', branch.name, rev]
-    if GitCommand(self, cmd).Wait() == 0:
-      branch.Save()
+    if exists:
+      if name == self.CurrentBranch:
+        return True
+      else:
+        cmd = ['checkout', name, '--']
+        return GitCommand(self, cmd).Wait() == 0
+
     else:
-      raise GitError('%s checkout %s ' % (self.name, rev))
+      branch = self.GetBranch(name)
+      branch.remote = self.GetRemote(self.remote.name)
+      branch.merge = self.revision
+
+      rev = branch.LocalMerge
+      cmd = ['checkout', '-b', branch.name, rev]
+      if GitCommand(self, cmd).Wait() == 0:
+        branch.Save()
+        return True
+      else:
+        return False
 
   def CheckoutBranch(self, name):
     """Checkout a local topic branch.
diff --git a/subcmds/init.py b/subcmds/init.py
index d86c49a..a32eaae 100644
--- a/subcmds/init.py
+++ b/subcmds/init.py
@@ -131,7 +131,9 @@
 
     m.Sync_LocalHalf()
     if is_new or m.CurrentBranch is None:
-      m.StartBranch('default')
+      if not m.StartBranch('default'):
+        print >>sys.stderr, 'fatal: cannot create default in manifest'
+        sys.exit(1)
 
   def _LinkManifest(self, name):
     if not name:
diff --git a/subcmds/start.py b/subcmds/start.py
index 4eb3e47..deced7c 100644
--- a/subcmds/start.py
+++ b/subcmds/start.py
@@ -47,5 +47,13 @@
       print >>sys.stderr, "error: '%s' is not a valid name" % nb
       sys.exit(1)
 
+    err = []
     for project in self.GetProjects(args[1:]):
-      project.StartBranch(nb)
+      if not project.StartBranch(nb):
+        err.append(project)
+
+    if err:
+      err.sort()
+      for p in err:
+        print >>sys.stderr, "error: cannot start in %s" % p.relpath
+      sys.exit(1)