diff --git a/src/utils.cpp b/src/utils.cpp
index b2befd4..294980a 100644
--- a/src/utils.cpp
+++ b/src/utils.cpp
@@ -175,6 +175,7 @@ std::any Add(std::any a, std::any b) {
     throw FatalError("Add: Type Error", 38);
 }
 std::any Sub(std::any a, std::any b) {
+  if (std::any_cast<std::string>(&a) != nullptr) a = ZYM::int2048(0);
   if (std::any_cast<std::string>(&b) != nullptr) b = ZYM::int2048(0);
   if (std::any_cast<NoneType>(&a)) a = (bool)false;
   if (std::any_cast<NoneType>(&b)) b = (bool)false;