diff --git a/src/calibre/ebooks/mobi/reader.py b/src/calibre/ebooks/mobi/reader.py
index d2bc25f8eb..972b049643 100644
--- a/src/calibre/ebooks/mobi/reader.py
+++ b/src/calibre/ebooks/mobi/reader.py
@@ -477,8 +477,8 @@ class MobiReader(object):
         self.processed_html = self.processed_html.replace('<mbp: ', '<mbp:')
         self.processed_html = re.sub(r'<?xml[^>]*>', '', self.processed_html)
         # Rearrange various style tags & paragraph tags so that lxml and BeautifulSoup don't get upset
-        self.processed_html = re.sub(r'(?i)(?P<styletags>(<(i|b|u|em|small|tt)>\s*){1,})(?P<para><p[^>]*>)', '\g<para>'+'\g<styletags>', self.processed_html)
-        self.processed_html = re.sub(r'(?i)(?P<para></p[^>]*>)\s*(?P<styletags>(</(i|b|u|em|small|tt)>\s*){1,})', '\g<styletags>'+'\g<para>', self.processed_html)
+        self.processed_html = re.sub(r'(?i)(?P<styletags>(<(i|b|u|em|small|big|strong|tt)>\s*){1,})(?P<para><p[^>]*>)', '\g<para>'+'\g<styletags>', self.processed_html)
+        self.processed_html = re.sub(r'(?i)(?P<para></p[^>]*>)\s*(?P<styletags>(</(i|b|u|em|small|big|strong|tt)>\s*){1,})', '\g<styletags>'+'\g<para>', self.processed_html)
 
     def remove_random_bytes(self, html):
         return re.sub('\x14|\x15|\x19|\x1c|\x1d|\xef|\x12|\x13|\xec|\x08',