diff --git a/src/simulation/m_viscous.fpp b/src/simulation/m_viscous.fpp
index 177b8c6bb4..d62e1f7ce9 100644
--- a/src/simulation/m_viscous.fpp
+++ b/src/simulation/m_viscous.fpp
@@ -985,7 +985,7 @@ contains
                         call s_compute_fd_gradient(q_prim_qp%vf(i), &
                                                    dq_prim_dx_qp(1)%vf(i), &
                                                    dq_prim_dy_qp(1)%vf(i), &
-                                                   dq_prim_dy_qp(1)%vf(i))
+                                                   dq_prim_dz_qp(1)%vf(i))
                     end do
 
                 end if