diff --git a/CHANGELOG b/CHANGELOG
index 0a5bab6..17f37ce 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -68,4 +68,4 @@
 0.10
 - In optimizer, added a function that tokenizes an expression
 - Document about complexity of operations
-- Bug: error in rename operator, it didn't perform a fullcopy of the relation
\ No newline at end of file
+- Bug: error in update operation, it changed the original tuple, so also other relations using the same tuple would change. Now it copies it.
\ No newline at end of file
diff --git a/complexity b/complexity
index ad01302..a7224a1 100644
--- a/complexity
+++ b/complexity
@@ -122,5 +122,5 @@ Notation
 
 2.9  Join 
 
-   Same as above.  
+   Same as above.
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diff --git a/relational/relation.py b/relational/relation.py
index 98d4bb0..f208179 100644
--- a/relational/relation.py
+++ b/relational/relation.py
@@ -446,8 +446,14 @@ class relation (object):
                     attributes[self.header.attributes[j]]=i[j]
             if eval(expr,attributes): #If expr is true, changing the tuple
                 affected+=1
+                new_tuple=list(i)
+                #Deleting the tuple, instead of changing it, so other
+                #relations can still point to the same list without
+                #being affected.
+                self.content.remove(i) 
                 for k in range(len(keys)):
-                    i[f_ids[k]]=str(dic[keys[k]])
+                    new_tuple[f_ids[k]]=str(dic[keys[k]])
+                self.content.append(new_tuple)
         return affected
     def insert(self,values):
         '''Inserts a tuple in the relation.