diff --git a/cros_update.py b/cros_update.py
index 3239ce4..5920cbe 100644
--- a/cros_update.py
+++ b/cros_update.py
@@ -151,7 +151,8 @@
 
     The auto update includes 4 steps:
     1. if devserver cannot run, restore the stateful partition.
-    2. if possible, do stateful update first, but never raise errors.
+    2. if possible, do stateful update first, but never raise errors, except
+       for timeout_util.TimeoutError caused by system.signal.
     3. If required or stateful_update fails, first do rootfs update, then do
        stateful_update.
     4. Post-check for the whole update.
@@ -193,6 +194,8 @@
               self._StatefulUpdate(chromeos_AU)
               stateful_update_complete = True
 
+        except timeout_util.TimeoutError:
+          raise
         except Exception as e:
           logging.debug('Error happens in stateful update: %r', e)