diff --git a/blackbox.c b/blackbox.c
index f8d6b27..7918c53 100644
--- a/blackbox.c
+++ b/blackbox.c
@@ -305,7 +305,7 @@ struct game_state {
 
 #define GRID(s,x,y) ((s)->grid[(y)*((s)->w+2) + (x)])
 
-#define RANGECHECK(s,x) ((x) >= 0 && (x) <= (s)->nlasers)
+#define RANGECHECK(s,x) ((x) >= 0 && (x) < (s)->nlasers)
 
 /* specify numbers because they must match array indexes. */
 enum { DIR_UP = 0, DIR_RIGHT = 1, DIR_DOWN = 2, DIR_LEFT = 3 };