diff --git a/src/calibre/devices/prs505/driver.py b/src/calibre/devices/prs505/driver.py
index bbda8f95d2..8d505683aa 100644
--- a/src/calibre/devices/prs505/driver.py
+++ b/src/calibre/devices/prs505/driver.py
@@ -147,6 +147,7 @@ class PRS505(Device):
             
     
     def open_windows(self):
+        time.sleep(6)
         drives = []
         wmi = __import__('wmi', globals(), locals(), [], -1) 
         c = wmi.WMI()
diff --git a/src/calibre/devices/usbms/device.py b/src/calibre/devices/usbms/device.py
index a33d041b2a..761fe9ba74 100644
--- a/src/calibre/devices/usbms/device.py
+++ b/src/calibre/devices/usbms/device.py
@@ -172,6 +172,7 @@ class Device(_Device):
         return prefix
 
     def open_windows(self):
+        time.sleep(6)
         drives = {}
         wmi = __import__('wmi', globals(), locals(), [], -1)
         c = wmi.WMI()