--- gimp-2.6.6/plug-ins/map-object/map-object-shade.c	2008-09-25 20:00:47.000000000 +0200
+++ plug-ins/map-object/map-object-shade.c	2009-08-10 17:27:19.000000000 +0200
@@ -76,7 +76,7 @@ phong_shade (GimpVector3 *pos,
 
       gimp_vector3_mul (&N, NL);
       gimp_vector3_sub (&NN, &N, &L);
-      RV = gimp_vector3_inner_product (&NN, &V);
+      RV = MAX (0., gimp_vector3_inner_product (&NN, &V));
       RV = pow (RV, mapvals.material.highlight);
 
       /* Compute diffuse and specular intensity contribution */
