diff --git a/relational/relation.py b/relational/relation.py
index 98d4bb0..27041e4 100644
--- a/relational/relation.py
+++ b/relational/relation.py
@@ -189,7 +189,9 @@ class relation (object):
             if (newt.header.rename(old,new)) == False:
                 return None
         
-        newt.content=list(self.content)
+        newt.content=[]
+        for i in self.content:
+            newt.content.append(list(i))
         return newt
         
     def intersection(self,other):