diff --git a/xmlrpc/README.txt b/xmlrpc/README.txt
index 5c8aa9d..5f7b15d 100755
--- a/xmlrpc/README.txt
+++ b/xmlrpc/README.txt
@@ -158,11 +158,17 @@ Updating the concept map
 
   >>> zopeId = xrf.getObjectByName('zope')['id']
   >>> zope3Id = xrf.getObjectByName('zope3')['id']
-  >>> xrf.assignChild(zopeId, zope3Id, defaultPred['id'])
+  >>> xrf.assignChild(zopeId, defaultPred['id'], zope3Id)
   'OK'
+  >>> pa = xrf.getParents(zope3Id)
+  >>> len(pa)
+  2
 
-  >>> xrf.deassignChild(zopeId, zope3Id, defaultPred['id'])
+  >>> xrf.deassignChild(zopeId, defaultPred['id'], zope3Id)
   'OK'
+  >>> pa = xrf.getParents(zope3Id)
+  >>> len(pa)
+  1
 
   >>> topicId = xrf.getObjectByName('topic')['id']
   >>> xrf.createConcept(topicId, u'zope2', u'Zope 2')
@@ -176,6 +182,12 @@ parameter is empty, the name will be generated from the title.
   {'description': u'', 'title': u'Python', 'type': '24', 'id': '58',
    'name': u'python'}
 
+If we try to deassign a ``hasType`` relation nothing will happen; a
+corresponding error value will be returned.
+
+  >>> xrf.deassignChild(topicId, typePred['id'], zope3Id)
+  'Not allowed'
+
 Changing the attributes of a concept
 ------------------------------------
 
diff --git a/xmlrpc/common.py b/xmlrpc/common.py
index f46f6b3..1cdcd33 100644
--- a/xmlrpc/common.py
+++ b/xmlrpc/common.py
@@ -120,15 +120,19 @@ class LoopsMethods(MethodPublisher, I18NView):
         return mapping
 
     def assignChild(self, objId, predicateId, childId):
-        obj = getObjectForUid(objId)
         pred = getObjectForUid(predicateId)
+        if pred == self.typePredicate:
+            return 'Not allowed'
+        obj = getObjectForUid(objId)
         child = getObjectForUid(childId)
         obj.assignChild(child, pred)
         return 'OK'
 
     def deassignChild(self, objId, predicateId, childId):
-        obj = getObjectForUid(objId)
         pred = getObjectForUid(predicateId)
+        if pred == self.typePredicate:
+            return 'Not allowed'
+        obj = getObjectForUid(objId)
         child = getObjectForUid(childId)
         obj.deassignChild(child, [pred])
         return 'OK'