diff --git a/src/calibre/devices/usbms/books.py b/src/calibre/devices/usbms/books.py
index 4a74f68349..9e19e9c66d 100644
--- a/src/calibre/devices/usbms/books.py
+++ b/src/calibre/devices/usbms/books.py
@@ -237,7 +237,10 @@ class CollectionsBookList(BookList):
                 return 1
             if y is None:
                 return -1
-            c = cmp(sort_key(x), sort_key(y))
+            if isinstance(x, unicode):
+                c = cmp(sort_key(x), sort_key(y))
+            else:
+                c = cmp(x, y)
             if c != 0:
                 return c
             # same as above -- no sort_key needed here