diff --git a/src/calibre/devices/scanner.py b/src/calibre/devices/scanner.py
index 9919648d94..5fab1be2f6 100644
--- a/src/calibre/devices/scanner.py
+++ b/src/calibre/devices/scanner.py
@@ -44,7 +44,7 @@ class DeviceScanner(object):
             return True
         for c in bcd:
             # Bug in winutil.get_usb_devices converts a to :
-            rev = ('rev_%4.4x'%c).replace(':', 'a')
+            rev = ('rev_%4.4x'%c).replace('a', ':')
             if rev in device_id:
                 return True
         return False