diff --git a/src/calibre/ebooks/oeb/polish/main.py b/src/calibre/ebooks/oeb/polish/main.py
index f8070bacf9..af30ac1e30 100644
--- a/src/calibre/ebooks/oeb/polish/main.py
+++ b/src/calibre/ebooks/oeb/polish/main.py
@@ -15,6 +15,7 @@ from calibre.ebooks.oeb.polish.container import get_container
 from calibre.ebooks.oeb.polish.stats import StatsCollector
 from calibre.ebooks.oeb.polish.subset import subset_all_fonts, iter_subsettable_fonts
 from calibre.ebooks.oeb.polish.images import compress_images
+from calibre.ebooks.oeb.polish.upgrade import upgrade_book
 from calibre.ebooks.oeb.polish.embed import embed_all_fonts
 from calibre.ebooks.oeb.polish.cover import set_cover
 from calibre.ebooks.oeb.polish.replace import smarten_punctuation
@@ -33,6 +34,7 @@ ALL_OPTS = {
     'smarten_punctuation':False,
     'remove_unused_css':False,
     'compress_images': False,
+    'upgrade_book': False,
 }
 
 CUSTOMIZATION = {
@@ -112,6 +114,10 @@ that need to parse them all.</p>
 affecting image quality.</p>
 '''),
 
+'upgrade_book': _('''\
+<p>Upgrade the internal structures of the book, if possible. For instance,
+upgrades EPUB 2 books to EPUB 3 books.</p>
+'''),
 }
 
 
@@ -225,6 +231,12 @@ def polish_one(ebook, opts, report, customization=None):
             changed = True
         report('')
 
+    if opts.upgrade_book:
+        rt(_('Upgrading book, if possible'))
+        if upgrade_book(ebook, report):
+            changed = True
+        report('')
+
     return changed
 
 
@@ -292,6 +304,7 @@ def option_parser():
     o('--smarten-punctuation', '-p', help=CLI_HELP['smarten_punctuation'])
     o('--remove-unused-css', '-u', help=CLI_HELP['remove_unused_css'])
     o('--compress-images', '-i', help=CLI_HELP['compress_images'])
+    o('--upgrade-book', '-U', help=CLI_HELP['upgrade_book'])
 
     o('--verbose', help=_('Produce more verbose output, useful for debugging.'))