diff --git a/sat/memory/disco.py b/sat/memory/disco.py
index 25ec4055..0fec5ce2 100755
--- a/sat/memory/disco.py
+++ b/sat/memory/disco.py
@@ -87,6 +87,9 @@ class HashManager(object):
             for hash_, xml in hashes.items():
                 element = xml_tools.ElementParser()(xml)
                 disco_info = disco.DiscoInfo.fromElement(element)
+                for ext_form in disco_info.extensions.values():
+                    # wokkel doesn't call typeCheck on reception, so we do it here
+                    ext_form.typeCheck()
                 if not disco_info.features and not disco_info.identities:
                     log.warning(
                         _(
@@ -180,6 +183,12 @@ class Discovery(object):
             # capability hash is not available, we'll compute one
             def infosCb(disco_infos):
                 cap_hash = self.generateHash(disco_infos)
+                for ext_form in disco_infos.extensions.values():
+                    # wokkel doesn't call typeCheck on reception, so we do it here
+                    # to avoid ending up with incorrect types. We have to do it after
+                    # the hash has been generated (str value is needed to compute the
+                    # hash)
+                    ext_form.typeCheck()
                 self.hashes[cap_hash] = disco_infos
                 self.host.memory.updateEntityData(
                     jid_, C.ENTITY_CAP_HASH, cap_hash, profile_key=client.profile
@@ -405,7 +414,7 @@ class Discovery(object):
     def _discoInfos(
         self, entity_jid_s, node="", use_cache=True, profile_key=C.PROF_KEY_NONE
     ):
-        """ Discovery method for the bridge
+        """Discovery method for the bridge
         @param entity_jid_s: entity we want to discover
         @param use_cache(bool): if True, use cached data if available
         @param node(unicode): optional node to use