diff --git a/jax_sph/solver.py b/jax_sph/solver.py
index 8acac63..826297c 100644
--- a/jax_sph/solver.py
+++ b/jax_sph/solver.py
@@ -47,6 +47,7 @@ def rho_evol_riemann_fn(
         wall_mask_j,
         n_w_j,
         g_ext_i,
+        u_tilde_j,
         **kwargs,
     ):
         # Compute unit vector, above eq. (6), Zhang (2017)
@@ -61,9 +62,12 @@ def rho_evol_riemann_fn(
         rho_L = rho_i
 
         #  u_w from eq. (15), Yang (2020)
+        # u_d = 2 * u_i - u_j
+        u_d = 2 * u_i - u_tilde_j
         u_R = jnp.where(
             wall_mask_j == 1,
-            -u_L + 2 * jnp.dot(u_j, n_w_j),
+            # -u_L + 2 * jnp.dot(u_j, n_w_j),
+            jnp.dot(u_d, -n_w_j),
             jnp.dot(u_j, -e_ij),
         )
         p_R = jnp.where(wall_mask_j == 1, p_L + rho_L * jnp.dot(g_ext_i, -r_ij), p_j)
@@ -595,6 +599,10 @@ def forward(state, neighbors):
             )
             n_w = jnp.where(jnp.absolute(n_w) < EPS, 0.0, n_w)
 
+            ##### Riemann velocity BCs
+            if self.is_bc_trick and (self.solver == "RIE"):
+                u_tilde = self._Riemann_velocities(u, w_dist, fluid_mask, i_s, j_s, N)
+
             ##### Density summation or evolution
 
             # update evolution
@@ -621,6 +629,7 @@ def forward(state, neighbors):
                     wall_mask[j_s],
                     n_w[j_s],
                     g_ext[i_s],
+                    u_tilde[j_s],
                 )
                 drhodt = ops.segment_sum(temp, i_s, N) * fluid_mask
                 rho = rho + self.dt * drhodt
@@ -644,7 +653,7 @@ def forward(state, neighbors):
                 )
             elif self.is_bc_trick and (self.solver == "RIE"):
                 mask = self._free_weight(fluid_mask[i_s], tag[i_s])
-                u_tilde = self._Riemann_velocities(u, w_dist, fluid_mask, i_s, j_s, N)
+                # u_tilde = self._Riemann_velocities(u, w_dist, fluid_mask, i_s, j_s, N)
                 temperature = self._heat_bc(
                     fluid_mask[j_s], w_dist, temperature, i_s, j_s, tag, N
                 )