diff --git a/src/OrbitDecomposition.jl b/src/OrbitDecomposition.jl
index aeadd10..2cd28ec 100644
--- a/src/OrbitDecomposition.jl
+++ b/src/OrbitDecomposition.jl
@@ -251,6 +251,9 @@ function compute_orbit_data{T<:GroupElem}(logger, name::String, G::Nemo.Group, S
    info(logger, "dimensions = $dimensions")
    @assert dot(multiplicities, dimensions) == sizes[radius]
 
-   save(joinpath(name, "U_pis.jld"), "Uπs", Uπs, "spUπs", sparsify.(Uπs), "dims", dimensions)
+   save(joinpath(name, "U_pis.jld"),
+         "Uπs", Uπs,
+         "spUπs", sparsify!.(deepcopy(Uπs), check=true, verbose=true),
+         "dims", dimensions)
    return 0
 end