We characterise the frame morphisms \(f:L\rightarrow M\) that lift to frame maps \(\overline{f}:\textsf{S}_b(L)\rightarrow \textsf{S}_b(M)\) , where \(\textsf{S}_b(L)\) is the collection of joins of complemented sublocales of a frame L, or equivalently the Booleanization of the collection \(\textsf{S}(L)\) of all its sublocales. We do so by proving that \(\textsf{S}_b(L)\) is isomorphic to the Bruns–Lakser completion of the meet-semilattice formed by the locally closed sublocales, i.e. the sublocales of the form \(\mathfrak {c}(a)\cap \mathfrak {o}(b)\) for \(a,b\in L\) .