diff --git a/src/calibre/ebooks/conversion/preprocess.py b/src/calibre/ebooks/conversion/preprocess.py
index 14bfceac40..5f6402f746 100644
--- a/src/calibre/ebooks/conversion/preprocess.py
+++ b/src/calibre/ebooks/conversion/preprocess.py
@@ -265,7 +265,8 @@ class CSSPreProcessor(object):
 
     PAGE_PAT   = re.compile(r'@page[^{]*?{[^}]*?}')
     # Remove some of the broken CSS Microsoft products
-    # create
+    # create, slightly dangerous as it removes to end of line
+    # rather than semi-colon
     MS_PAT     = re.compile(r'^\s*(mso-|panose-).+?$',
             re.MULTILINE|re.IGNORECASE)