Comment #1 on issue 3407 by rydier: HashedCollection missed abstract method noCheckAdd: http://code.google.com/p/pharo/issues/detail?id=3407 Alternatively change #grow to read: self growTo: self growSize. and #rehash self growTo: array size. This would be part of the synch up with HashedCollection improvements from squeak, as described in http://code.google.com/p/pharo/issues/detail?id=2551 . IIRC, step one as mentioned there (and introduced in core) stopped just short of switching these two methods over (to not have to deal with load orders of simultaniously introduced growTo: ), all methods part of growTo: should already be in image, and work correctly.