diff --git a/src/calibre/ebooks/conversion/preprocess.py b/src/calibre/ebooks/conversion/preprocess.py
index 0adcb88cfd..14bfceac40 100644
--- a/src/calibre/ebooks/conversion/preprocess.py
+++ b/src/calibre/ebooks/conversion/preprocess.py
@@ -264,10 +264,16 @@ class Dehyphenator(object):
 class CSSPreProcessor(object):
 
     PAGE_PAT   = re.compile(r'@page[^{]*?{[^}]*?}')
+    # Remove some of the broken CSS Microsoft products
+    # create
+    MS_PAT     = re.compile(r'^\s*(mso-|panose-).+?$',
+            re.MULTILINE|re.IGNORECASE)
 
     def __call__(self, data, add_namespace=False):
         from calibre.ebooks.oeb.base import XHTML_CSS_NAMESPACE
         data = self.PAGE_PAT.sub('', data)
+        if '\n' in data:
+            data = self.MS_PAT.sub('', data)
         if not add_namespace:
             return data
         ans, namespaced = [], False