--- a/ImmutableByteArray.st	Mon Oct 03 12:44:41 2016 +0100
+++ b/ImmutableByteArray.st	Sun Oct 09 21:28:18 2016 +0100
@@ -206,6 +206,12 @@
     ^ self
 !
 
+beMutable
+    "you never go back"
+
+    ^ self shouldNotImplement
+!
+
 beUnsigned
     "that's what I am-"