diff --git a/src/calibre/devices/kobo/books.py b/src/calibre/devices/kobo/books.py
index 5a76ec2f63..8fd82ce4f1 100644
--- a/src/calibre/devices/kobo/books.py
+++ b/src/calibre/devices/kobo/books.py
@@ -161,6 +161,8 @@ class KTCollectionsBookList(CollectionsBookList):
 #                    debug_print("KTCollectionsBookList:get_collections - val is list=", val)
                 elif fm is not None and fm['datatype'] == 'series':
                     val = [orig_val]
+                elif fm is not None and fm['datatype'] == 'rating':
+                    val = [str(orig_val / 2)]
                 elif fm is not None and fm['datatype'] == 'text' and fm['is_multiple']:
                     if isinstance(orig_val, (list, tuple)):
                         val = orig_val
@@ -205,7 +207,7 @@ class KTCollectionsBookList(CollectionsBookList):
                     if not category:
                         continue
 
-                    cat_name = category.strip(' ,')
+                    cat_name = str(category).strip(' ,')
 
                     if cat_name not in collections:
                         collections[cat_name] = {}