diff --git a/src/calibre/ebooks/metadata/book/render.py b/src/calibre/ebooks/metadata/book/render.py
index 1325ce2d43..6b3f52e395 100644
--- a/src/calibre/ebooks/metadata/book/render.py
+++ b/src/calibre/ebooks/metadata/book/render.py
@@ -139,12 +139,13 @@ def mi_to_html(mi, field_list=None, default_author_link=None, use_roman_numbers=
             bpath = ''
             if path:
                 h, t = os.path.split(path)
-                bpath = '/'.join((os.path.basename(h), t))
+                bpath = os.sep.join((os.path.basename(h), t))
             data = ({
                 'fmt':x, 'path':a(path or ''), 'fname':a(mi.format_files.get(x, '')),
-                'ext':x.lower(), 'id':book_id, 'bpath':bpath,
+                'ext':x.lower(), 'id':book_id, 'bpath':bpath, 'sep':os.sep
             } for x in mi.formats)
-            fmts = [u'<a data-full-path="{path}/{fname}.{ext}" title="{bpath}/{fname}.{ext}" href="format:{id}:{fmt}">{fmt}</a>'.format(**x) for x in data]
+            fmts = [u'<a data-full-path="{path}{sep}{fname}.{ext}" title="{bpath}{sep}{fname}.{ext}" href="format:{id}:{fmt}">{fmt}</a>'.format(**x)
+                    for x in data]
             ans.append((field, row % (name, u', '.join(fmts))))
         elif field == 'identifiers':
             urls = urls_from_identifiers(mi.identifiers)