diff --git a/client/cros/power/sys_power.py b/client/cros/power/sys_power.py
index a2bfe26..3f4353f 100644
--- a/client/cros/power/sys_power.py
+++ b/client/cros/power/sys_power.py
@@ -144,6 +144,7 @@
     """
 
     # stop check_ethernet.hook from running until the test exits
+    global pause_ethernet_fd
     if pause_ethernet_fd == 0:
         # we don't write to the file - but we might need to create it.
         pause_ethernet_fd = open(PAUSE_ETHERNET_HOOK_FILE,'a+')