When a dynamic storage allocation scheme requires variable-length elements, an element of a given length may be requested when no free element large enough is available. This can happen even though the total free space is more than adequate to fulfil the request. In such a situation the program will fail unless some method is at hand for forming the available space into a single element large enough to satisfy the request. We present a procedure for compacting the store such that all of the free space forms a single element.