diff --git a/src/fluid/bcknd/cpu/pnpn_res_cpu.f90 b/src/fluid/bcknd/cpu/pnpn_res_cpu.f90
index 9b842fc6c202..87e2f8d5697c 100644
--- a/src/fluid/bcknd/cpu/pnpn_res_cpu.f90
+++ b/src/fluid/bcknd/cpu/pnpn_res_cpu.f90
@@ -92,7 +92,7 @@ subroutine pnpn_prs_res_cpu_compute(p, p_res, u, v, w, u_e, v_e, w_e, f_x, &
 
     call Ax%compute(p_res%x,p%x,c_Xh,p%msh,p%Xh)
 
-    do i = 1, n
+    do concurrent (i = 1:n)
        p_res%x(i,1,1,1) = (-p_res%x(i,1,1,1)) &
                         + wa1%x(i,1,1,1) + wa2%x(i,1,1,1) + wa3%x(i,1,1,1)
     end do
@@ -161,7 +161,7 @@ subroutine pnpn_vel_res_cpu_compute(Ax, u, v, w, u_res, v_res, w_res, &
 
     call opgrad(ta1%x, ta2%x, ta3%x, p%x, c_Xh)
 
-    do i = 1, n
+    do concurrent (i = 1:n)
        u_res%x(i,1,1,1) = (-u_res%x(i,1,1,1)) - ta1%x(i,1,1,1) + f_x%x(i,1,1,1)
        v_res%x(i,1,1,1) = (-v_res%x(i,1,1,1)) - ta2%x(i,1,1,1) + f_y%x(i,1,1,1)
        w_res%x(i,1,1,1) = (-w_res%x(i,1,1,1)) - ta3%x(i,1,1,1) + f_z%x(i,1,1,1)