diff --git a/src/python/espressomd/visualization.py b/src/python/espressomd/visualization.py
index fb750e014..3e8caa7b5 100644
--- a/src/python/espressomd/visualization.py
+++ b/src/python/espressomd/visualization.py
@@ -756,16 +756,20 @@ class openGLLive():
             self._update_lb_velocity_plane_gpu()
 
     def _update_lb_velocity_plane_cpu(self):
-        agrid = self.lb_params['agrid']
+        agrid = 10.
         self.lb_plane_vel = []
         ng = self.specs['LB_plane_ngrid']
+        ext_h_field = np.zeros(3)
+        for constraint in self.system.constraints:
+            if isinstance(constraint, espressomd.constraints.HomogeneousMagneticField):
+                ext_h_field += constraint.H
+        if np.linalg.norm(ext_h_field) < 1e-8:
+            return
         for xi in range(ng):
             for xj in range(ng):
                 pp = np.copy((self.lb_plane_p + xi * 1.0 / ng * self.lb_plane_b1 +
                               xj * 1.0 / ng * self.lb_plane_b2) % self.system.box_l)
-                i, j, k = (int(ppp / agrid) for ppp in pp)
-                lb_vel = np.copy(self.lb[i, j, k].velocity)
-                self.lb_plane_vel.append([pp, lb_vel])
+                self.lb_plane_vel.append([pp, ext_h_field])
 
     def _update_lb_velocity_plane_gpu(self):
         ng = self.specs['LB_plane_ngrid']