--- a/ImmutableString.st	Thu Aug 20 17:24:01 2015 +0200
+++ b/ImmutableString.st	Thu Aug 20 17:24:12 2015 +0200
@@ -208,6 +208,14 @@
     ^ super becomeNil
 
     "Created: / 3.8.1998 / 14:48:37 / cg"
+!
+
+becomeSameAs:anotherObject
+    "trigger an error if I should become something else
+     (this would be an even more tricky manipulation)"
+
+    self noModificationError.
+    ^ super becomeSameAs:anotherObject
 ! !
 
 !ImmutableString class methodsFor:'documentation'!