diff --git a/src/calibre/ebooks/mobi/reader.py b/src/calibre/ebooks/mobi/reader.py
index 2a31732f08..934e8476d2 100644
--- a/src/calibre/ebooks/mobi/reader.py
+++ b/src/calibre/ebooks/mobi/reader.py
@@ -693,12 +693,10 @@ class MobiReader(object):
             try:
                 lm = float(lm)
             except:
-                raise
                 lm = 0.0
             try:
                 ti = float(ti)
             except:
-                raise
                 ti = 0.0
             return lm + ti