diff --git a/src/calibre/devices/prs505/sony_cache.py b/src/calibre/devices/prs505/sony_cache.py
index f05d9c0311..879f86d66a 100644
--- a/src/calibre/devices/prs505/sony_cache.py
+++ b/src/calibre/devices/prs505/sony_cache.py
@@ -89,6 +89,10 @@ class XMLCache(object):
                         raw, strip_encoding_pats=True, assume_utf8=True,
                         verbose=DEBUG)[0],
                         parser=parser)
+            if self.roots[source_id] is None:
+                raise Exception(('The SONY database at %s is corrupted. Try '
+                        ' disconnecting and reconnecting your reader.')%path)
+
         # }}}
 
         recs = self.roots[0].xpath('//*[local-name()="records"]')