diff --git a/extra/boids/boids.factor b/extra/boids/boids.factor
index 397ce6eb5a..e703472e40 100644
--- a/extra/boids/boids.factor
+++ b/extra/boids/boids.factor
@@ -68,7 +68,9 @@ VAR: separation-radius
 
 ! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 
-: distance ( boid boid -- n ) boid-pos swap boid-pos v- norm ;
+! : distance ( boid boid -- n ) boid-pos swap boid-pos v- norm ;
+
+: distance ( boid boid -- n ) [ boid-pos ] [ boid-pos ] bi* v- norm ;
 
 ! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!