diff --git a/cpp/particles/particles_input_random.hpp b/cpp/particles/particles_input_random.hpp
index 9b874b59c8bfc29465477c14abaff1cf470695fd..1179b080f4079515b42d16e64a0de9daa7cb8af2 100644
--- a/cpp/particles/particles_input_random.hpp
+++ b/cpp/particles/particles_input_random.hpp
@@ -48,7 +48,7 @@ class particles_input_random: public abstract_particles_input<partsize_t, partic
     public:
         particles_input_random(
                 const MPI_Comm in_mpi_comm,
-                const int NPARTICLES,
+                const partsize_t NPARTICLES,
                 const int rseed,
                 const particle_rnumber my_spatial_low_limit,
                 const particle_rnumber my_spatial_up_limit):