diff --git a/src/trace.wgsl b/src/trace.wgsl
index 27afd3b..727b320 100644
--- a/src/trace.wgsl
+++ b/src/trace.wgsl
@@ -113,7 +113,8 @@ fn trace_fragment(in: Varying) -> vec3f {
 		let normal = (pos - s.center) / s.radius;
 		if (all(s.emit_color == vec3(0.))) {
 			color *= s.reflect_color;
-			let diffuse = normal + rand_sphere();
+			let sp = rand_sphere();
+			let diffuse = sign(dot(sp, normal)) * sp;
 			let specular = reflect(ray, normal);
 			ray = normalize(mix(diffuse, specular, s.glossiness));
 		} else {