diff --git a/Graphics/IsoSimplex.cpp b/Graphics/IsoSimplex.cpp
index ecaa56854790e80332a122c9764d85aaea40bc5c..1647fa3ec31ab8ebc99a92e4a23d97339e47b922 100644
--- a/Graphics/IsoSimplex.cpp
+++ b/Graphics/IsoSimplex.cpp
@@ -168,7 +168,7 @@ void IsoSimplex( Post_View *View,
     }
   }
 
-  if(nb < 3)return;
+  if(nb < 3 || nb > 4)return;
 
   EnhanceSimplexPolygon (View, nb, Xp, Yp, Zp, PVals, X, Y, Z, Val, norms, preproNormals);