diff --git a/bfps/cpp/particles/particles_distr_mpi.hpp b/bfps/cpp/particles/particles_distr_mpi.hpp
index 979c8d1e36c98fbe468e444dea9a2229d3c1f24f..32e8606665eaa3cd8e20aa3925514a7b67ac754b 100644
--- a/bfps/cpp/particles/particles_distr_mpi.hpp
+++ b/bfps/cpp/particles/particles_distr_mpi.hpp
@@ -830,7 +830,7 @@ public:
                     assert(current_my_nb_particles_per_partition[idxPartition] ==
                            current_offset_particles_for_partition[idxPartition+1] - current_offset_particles_for_partition[idxPartition]);
                     for(partsize_t idx = current_offset_particles_for_partition[idxPartition] ; idx < current_offset_particles_for_partition[idxPartition+1] ; ++idx){
-                        assert(in_computer.pbc_field_layer((*inout_positions_particles)[idx*3+IDX_Z], IDX_Z)-current_partition_interval.first == idxPartition);
+                        assert(in_computer.pbc_field_layer((*inout_positions_particles)[idx*size_particle_positions+IDX_Z], IDX_Z)-current_partition_interval.first == idxPartition);
                     }
                 }
             }