diff --git a/src/ludus/prelude.ld b/src/ludus/prelude.ld
index 3a0bb72..43013d2 100644
--- a/src/ludus/prelude.ld
+++ b/src/ludus/prelude.ld
@@ -369,7 +369,7 @@ fn sub {
 	(x as :number) -> x
 	(x as :number, y as :number) -> base :sub (x, y)
 	(x, y, ...zs) -> fold (base :sub, zs, base :sub (x, y))
-	((x1, y1), (x2, y2)) -> (base :sub (x1, x2), base :sub (x2, y2))
+	((x1, y1), (x2, y2)) -> (base :sub (x1, x2), base :sub (y1, y2))
 }
 
 fn mult {