diff --git a/extra/terrain/shaders/shaders.factor b/extra/terrain/shaders/shaders.factor
index bfb46b8ba1..e5b517ad59 100644
--- a/extra/terrain/shaders/shaders.factor
+++ b/extra/terrain/shaders/shaders.factor
@@ -8,11 +8,14 @@ varying vec3 direction;
 
 void main()
 {
-    vec4 v = vec4(gl_Vertex.xy, -1.0, 1.0);
+    vec4 v = vec4(gl_Vertex.xy, 1.0, 1.0);
     gl_Position = v;
+
+    vec4 p = (gl_ProjectionMatrixInverse * v) * vec4(1,1,-1,1);
+    
     float s = sin(sky_theta), c = cos(sky_theta);
     direction = mat3(1, 0, 0,  0, c, s,  0, -s, c)
-        * (gl_ModelViewMatrixInverse * vec4(v.xyz, 0.0)).xyz;
+        * (gl_ModelViewMatrixInverse * vec4(p.xyz, 0.0)).xyz;
 }
 
 ;