diff --git a/devel/mpn/mpn.irp.f b/devel/mpn/mpn.irp.f
index 1caa788..fa8c7c0 100644
--- a/devel/mpn/mpn.irp.f
+++ b/devel/mpn/mpn.irp.f
@@ -21,7 +21,11 @@ program mpn
   e_pert(1) = hf_energy - e_pert(0) - nuclear_repulsion
   do k=1,mp_order
     ! H_ij C^(k-1)
-    call h_s2_u_0_nstates_zmq(c_pert(1,k),s2,c_pert(1,k-1),1,N_det)
+    if (distributed_davidson) then
+        call H_S2_u_0_nstates_zmq   (c_pert(1,k),s2,c_pert(1,k-1),1,N_det)
+    else
+        call H_S2_u_0_nstates_openmp(c_pert(1,k),s2,c_pert(1,k-1),1,N_det)
+    endif
     if (k>1) then
       e_pert(k) += c_pert(1,k)
     endif