diff --git a/src/calibre/devices/prst1/driver.py b/src/calibre/devices/prst1/driver.py
index 4cbe9b4994..7291d5dbcb 100644
--- a/src/calibre/devices/prst1/driver.py
+++ b/src/calibre/devices/prst1/driver.py
@@ -380,7 +380,7 @@ class PRST1(USBMS):
         # Record what the max id being used is as well.
         db_books = {}
         for i, row in enumerate(cursor):
-            if row[0] is None:
+            if not hasattr(row[0], 'replace'):
                 continue
             lpath = row[0].replace('\\', '/')
             db_books[lpath] = row[1]