--- a/ImmutableByteArray.st	Tue Oct 04 12:43:26 2016 +0200
+++ b/ImmutableByteArray.st	Tue Oct 04 12:43:33 2016 +0200
@@ -206,6 +206,12 @@
     ^ self
 !
 
+beMutable
+    "you never go back"
+
+    ^ self shouldNotImplement
+!
+
 beUnsigned
     "that's what I am-"