diff --git a/src/calibre/gui2/actions/polish.py b/src/calibre/gui2/actions/polish.py
index 69c8d6fc23..b77849d882 100644
--- a/src/calibre/gui2/actions/polish.py
+++ b/src/calibre/gui2/actions/polish.py
@@ -432,7 +432,20 @@ class PolishAction(InterfaceAction):
             return None
         db = self.gui.library_view.model().db
         ans = (db.id(r) for r in rows)
-        return self.get_supported_books(ans)
+        ans = self.get_supported_books(ans)
+        for fmts in ans.itervalues():
+            for x in fmts:
+                if x.startswith('ORIGINAL_'):
+                    from calibre.gui2.dialogs.confirm_delete import confirm
+                    if not confirm(_(
+                            'One of the books you are polishing has an {0} format.'
+                            ' Polishing will use this as the source and overwrite'
+                            ' any existing {1} format. Are you sure you want to proceed?').format(
+                                x, x[len('ORIGINAL_'):]), 'confirm_original_polish', title=_('Are you sure?'),
+                                   confirm_msg=_('Ask for this confirmation again')):
+                        return {}
+                    break
+        return ans
 
     def get_supported_books(self, book_ids):
         from calibre.ebooks.oeb.polish.main import SUPPORTED