diff --git a/grid.cc b/grid.cc
index 16efb1384..762d3d558 100644
--- a/grid.cc
+++ b/grid.cc
@@ -2024,7 +2024,9 @@ static void setup_grid_cartesian_3d()
   // have a higher expansion velocity than the sides
   const double vmax_corner = sqrt(3 * pow(globals::vmax, 2));
   printout("corner vmax %g [cm/s] (%.2fc)\n", vmax_corner, vmax_corner / CLIGHT);
-  assert_always(vmax_corner < CLIGHT);
+  if (!FORCE_SPHERICAL_ESCAPE_SURFACE) {
+    assert_always(vmax_corner < CLIGHT);
+  }
 
   /// Set grid size for uniform xyz grid
   if (get_model_type() == GRID_CARTESIAN3D) {