diff --git a/bin/addons/base/ir/ir_model.py b/bin/addons/base/ir/ir_model.py
index aa89e0f71dd..c96044d2918 100644
--- a/bin/addons/base/ir/ir_model.py
+++ b/bin/addons/base/ir/ir_model.py
@@ -408,6 +408,9 @@ class ir_model_data(osv.osv):
         'date_update': lambda *a: time.strftime('%Y-%m-%d %H:%M:%S'),
         'noupdate': lambda *a: False
     }
+    _sql_constraints = [
+        ('module_name_uniq', 'unique(name, module)', 'You can not have multiple records with the same id for the same module'),
+    ]
 
     def __init__(self, pool, cr):
         osv.osv.__init__(self, pool, cr)
@@ -415,11 +418,13 @@ class ir_model_data(osv.osv):
         self.doinit = True
         self.unlink_mark = {}
 
-    def _get_id(self,cr, uid, module, xml_id):
+    @tools.cache()
+    def _get_id(self, cr, uid, module, xml_id):
         ids = self.search(cr, uid, [('module','=',module),('name','=', xml_id)])
-        assert len(ids)==1, '%d reference(s) to %s.%s. You should have one and only one !' % (len(ids), module, xml_id)
+        if not ids:
+            raise Exception('No references to %s.%s' % (module, xml_id))
+        # the sql constraints ensure us we have only one result
         return ids[0]
-    _get_id = tools.cache(skiparg=2)(_get_id)
 
     def _update_dummy(self,cr, uid, model, module, xml_id=False, store=True):
         if not xml_id:
diff --git a/bin/tools/convert.py b/bin/tools/convert.py
index fb85c4b88f2..220b272f4dd 100644
--- a/bin/tools/convert.py
+++ b/bin/tools/convert.py
@@ -256,7 +256,11 @@ form: module.record_id""" % (xml_id,)
         if len(d_search):
             ids = self.pool.get(d_model).search(cr,self.uid,eval(d_search))
         if len(d_id):
-            ids.append(self.id_get(cr, d_model, d_id))
+            try:
+                ids.append(self.id_get(cr, d_model, d_id))
+            except:
+                # d_id cannot be found. doesn't matter in this case
+                pass
         if len(ids):
             self.pool.get(d_model).unlink(cr, self.uid, ids)
             self.pool.get('ir.model.data')._unlink(cr, self.uid, d_model, ids, direct=True)