--- a/src/octree.cc	Thu May 08 09:21:25 2008 +0200
+++ b/src/octree.cc	Sat May 10 14:29:37 2008 +0200
@@ -148,7 +148,7 @@
 	}
 }
 
-Shape * Octree::nearest_intersection(const Shape *origin_shape, const Ray &ray,
+const Shape * Octree::nearest_intersection(const Shape *origin_shape, const Ray &ray,
 		Float &nearest_distance)
 {
 	/* if we have no tree, fall back to naive test */
@@ -217,7 +217,7 @@
 	node = root;
 	st_cur->next = -1;
 
-	Shape *nearest_shape = NULL;
+	const Shape *nearest_shape = NULL;
 	for (;;)
 	{
 		if (st_cur->next == -1)