diff --git a/attributs.py b/attributs.py
index aebe1dd..4239d0d 100644
--- a/attributs.py
+++ b/attributs.py
@@ -272,6 +272,8 @@ class Attr(object):
         self.parse_value(val)
 
     def __hash__(self):
+        if not self.parent or self.parent.mode in ['w', 'rw']:
+            raise TypeError("Mutable structure are not hashable, please use mode = 'ro' to do so")
         if hasattr(self.value, "__hash__") and self.value.__hash__ is not None:
             return self.value.__hash__()
         else:
diff --git a/objets.py b/objets.py
index 7ebc0d5..7954a10 100644
--- a/objets.py
+++ b/objets.py
@@ -174,6 +174,24 @@ class CransLdapObject(object):
         else:
             return False
 
+    def __hash__(self):
+        if self.mode in ['w', 'rw']:
+            raise TypeError("Mutable structure are not hashable, please use mode = 'ro' to do so")
+        def c_mul(a, b):
+            return eval(hex((long(a) * b) & 0xFFFFFFFFL)[:-1])
+        value = 0x345678
+        l=0
+        keys = self.keys()
+        keys.sort()
+        for key in keys:
+            l+=len(self.attrs[key])
+            for item in self.attrs[key]:
+                value = c_mul(1000003, value) ^ hash(item)
+        value = value ^ l
+        if value == -1:
+            value = -2
+        return value
+
     def __iter__(self):
         if self.mode in [ 'w', 'rw' ]:
             return self._modifs.__iter__()