diff --git a/ubb-vga/tstimg.c b/ubb-vga/tstimg.c
index fc35e25..a5e7330 100644
--- a/ubb-vga/tstimg.c
+++ b/ubb-vga/tstimg.c
@@ -86,15 +86,15 @@ static void grill(void **f, int ares, int bres, int swap)
 	int n, o;
 	int i, a, b;
 
-	n = ares/GRID+1;
-	o = (ares % GRID)/2;
+	n = (ares-1)/GRID+1;
+	o = ((ares-1) % GRID)/2;
 	if (!(n & 1)) {
 		n--;
 		o += GRID/2;
 	}
 	for (i = 0; i != n; i++) {
 		a = o+i*GRID;
-		for (b = 0; b != bres; b++)
+		for (b = 0; b != bres-1; b++)
 			if (swap)
 				pixel(f, bres, b, a, WHITE);
 			else