diff --git a/src/calibre/ebooks/conversion/plumber.py b/src/calibre/ebooks/conversion/plumber.py
index 3a18b40539..defb2b837d 100644
--- a/src/calibre/ebooks/conversion/plumber.py
+++ b/src/calibre/ebooks/conversion/plumber.py
@@ -693,6 +693,8 @@ OptionRecommendation(name='sr3_replace',
     def unarchive(self, path, tdir):
         extract(path, tdir)
         files = list(walk(tdir))
+        files = [f if isinstance(f, unicode) else f.decode(filesystem_encoding)
+                for f in files]
         from calibre.customize.ui import available_input_formats
         fmts = available_input_formats()
         for x in ('htm', 'html', 'xhtm', 'xhtml'): fmts.remove(x)