diff --git a/src/calibre/ebooks/oeb/polish/main.py b/src/calibre/ebooks/oeb/polish/main.py
index f2f5287a6b..dd5a410be2 100644
--- a/src/calibre/ebooks/oeb/polish/main.py
+++ b/src/calibre/ebooks/oeb/polish/main.py
@@ -42,8 +42,8 @@ changes needed for the desired effect.</p>
 
 <p>You should use this tool as the last step in your ebook creation process.</p>
 
-<p>Note that polishing only works on files in the <b>%s</b> formats.</p>
-''')%_(' or ').join(SUPPORTED),
+<p>Note that polishing only works on files in the %s formats.</p>
+''')%_(' or ').join('<b>%s</b>'%x for x in SUPPORTED),
 
 'subset': _('''\
 <p>Subsetting fonts means reducing an embedded font to contain