From 44b81fd9a2034345700e21cb6a957c625c9c67b6 Mon Sep 17 00:00:00 2001
From: Shunsuke Shibayama <sbym1346@gmail.com>
Date: Sat, 29 Oct 2022 10:53:30 +0900
Subject: [PATCH] Update free.rs

---
 compiler/erg_compiler/ty/free.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/compiler/erg_compiler/ty/free.rs b/compiler/erg_compiler/ty/free.rs
index 9c8c12ac..33f9e548 100644
--- a/compiler/erg_compiler/ty/free.rs
+++ b/compiler/erg_compiler/ty/free.rs
@@ -47,7 +47,7 @@ pub trait HasLevel {
     }
     fn lift(&self) {
         if let Some(lev) = self.level() {
-            self.set_level(lev + 1);
+            self.set_level(lev.saturating_add(1));
         }
     }
     fn generalize(&self) {