diff --git a/src/calibre/ebooks/mobi/reader/mobi8.py b/src/calibre/ebooks/mobi/reader/mobi8.py
index b6fe7d9aa0..8938b103d3 100644
--- a/src/calibre/ebooks/mobi/reader/mobi8.py
+++ b/src/calibre/ebooks/mobi/reader/mobi8.py
@@ -464,7 +464,7 @@ class Mobi8Reader(object):
             start = None
             reached = True
         if frag:
-            elems = XPath('//*[@id="%s"]'%frag)
+            elems = XPath('//*[@id="%s"]'%frag)(root)
             if elems:
                 start = elems[0]