sed - replacing a substring containing a hyphen

I'm attempting to replace a substring that contains a hyphen and not having much success, can anyone point out where i'm going wrong or suggest an alternative.

[root@localhost kvm]#  echo /var/lib/libvirt/images/vm888b-clone.qcow | sed -e 's|vm888-clone|qaz|g'
/var/lib/libvirt/images/vm888b-clone.qcow
sed -e 's|vm888b-clone|qaz|g'