diff --git a/weboob/tools/parsers/html5libparser.py b/weboob/tools/parsers/html5libparser.py
index 400c0151..4bf73de4 100644
--- a/weboob/tools/parsers/html5libparser.py
+++ b/weboob/tools/parsers/html5libparser.py
@@ -47,6 +47,5 @@ class Html5libParser(HTMLParser, IParser):
     def parse(self, data, encoding):
         return HTMLParser.parse(self, data, encoding=encoding)
 
-    def tostring(self, elem):
-        # TODO
-        raise NotImplementedError()
+    def tostring(self, element):
+        return element.toxml()