diff --git a/subcmds/sync.py b/subcmds/sync.py
index 36ef16db..eac0556d 100644
--- a/subcmds/sync.py
+++ b/subcmds/sync.py
@@ -39,6 +39,10 @@ from project import R_HEADS
 from project import SyncBuffer
 from progress import Progress
 
+class _FetchError(Exception):
+  """Internal error thrown in _FetchHelper() when we don't want stack trace."""
+  pass
+
 class Sync(Command, MirrorSafeCommand):
   jobs = 1
   common = True
@@ -135,20 +139,60 @@ later is required to fix a server side protocol bug.
                  dest='repo_upgraded', action='store_true',
                  help=SUPPRESS_HELP)
 
-  def _FetchHelper(self, opt, project, lock, fetched, pm, sem):
-      if not project.Sync_NetworkHalf(quiet=opt.quiet):
-        print >>sys.stderr, 'error: Cannot fetch %s' % project.name
-        if opt.force_broken:
-          print >>sys.stderr, 'warn: --force-broken, continuing to sync'
-        else:
-          sem.release()
-          sys.exit(1)
+  def _FetchHelper(self, opt, project, lock, fetched, pm, sem, err_event):
+      """Main function of the fetch threads when jobs are > 1.
 
-      lock.acquire()
-      fetched.add(project.gitdir)
-      pm.update()
-      lock.release()
-      sem.release()
+      Args:
+        opt: Program options returned from optparse.  See _Options().
+        project: Project object for the project to fetch.
+        lock: Lock for accessing objects that are shared amongst multiple
+            _FetchHelper() threads.
+        fetched: set object that we will add project.gitdir to when we're done
+            (with our lock held).
+        pm: Instance of a Project object.  We will call pm.update() (with our
+            lock held).
+        sem: We'll release() this semaphore when we exit so that another thread
+            can be started up.
+        err_event: We'll set this event in the case of an error (after printing
+            out info about the error).
+      """
+      # We'll set to true once we've locked the lock.
+      did_lock = False
+
+      # Encapsulate everything in a try/except/finally so that:
+      # - We always set err_event in the case of an exception.
+      # - We always make sure we call sem.release().
+      # - We always make sure we unlock the lock if we locked it.
+      try:
+        success = project.Sync_NetworkHalf(quiet=opt.quiet)
+
+        # Lock around all the rest of the code, since printing, updating a set
+        # and Progress.update() are not thread safe.
+        lock.acquire()
+        did_lock = True
+
+        if not success:
+          print >>sys.stderr, 'error: Cannot fetch %s' % project.name
+          if opt.force_broken:
+            print >>sys.stderr, 'warn: --force-broken, continuing to sync'
+          else:
+            raise _FetchError()
+
+        fetched.add(project.gitdir)
+        pm.update()
+      except BaseException, e:
+        # Notify the _Fetch() function about all errors.
+        err_event.set()
+
+        # If we got our own _FetchError, we don't want a stack trace.
+        # However, if we got something else (something in Sync_NetworkHalf?),
+        # we'd like one (so re-raise after we've set err_event).
+        if not isinstance(e, _FetchError):
+          raise
+      finally:
+        if did_lock:
+          lock.release()
+        sem.release()
 
   def _Fetch(self, projects, opt):
     fetched = set()
@@ -169,7 +213,13 @@ later is required to fix a server side protocol bug.
       threads = set()
       lock = _threading.Lock()
       sem = _threading.Semaphore(self.jobs)
+      err_event = _threading.Event()
       for project in projects:
+        # Check for any errors before starting any new threads.
+        # ...we'll let existing threads finish, though.
+        if err_event.is_set():
+          break
+
         sem.acquire()
         t = _threading.Thread(target = self._FetchHelper,
                               args = (opt,
@@ -177,13 +227,19 @@ later is required to fix a server side protocol bug.
                                       lock,
                                       fetched,
                                       pm,
-                                      sem))
+                                      sem,
+                                      err_event))
         threads.add(t)
         t.start()
 
       for t in threads:
         t.join()
 
+      # If we saw an error, exit with code 1 so that other scripts can check.
+      if err_event.is_set():
+        print >>sys.stderr, '\nerror: Exited sync due to fetch errors'
+        sys.exit(1)
+
     pm.end()
     for project in projects:
       project.bare_git.gc('--auto')