diff --git a/crates/erg_compiler/context/initialize/funcs.rs b/crates/erg_compiler/context/initialize/funcs.rs
index 5e9929c90..e3b4888fc 100644
--- a/crates/erg_compiler/context/initialize/funcs.rs
+++ b/crates/erg_compiler/context/initialize/funcs.rs
@@ -5,7 +5,7 @@ use erg_common::log;
 use crate::ty::constructors::*;
 use crate::ty::typaram::TyParam;
 use crate::ty::value::ValueObj;
-use crate::ty::{CastTarget, Field, GuardType, Type, Visibility};
+use crate::ty::{CastTarget, Field, Type, Visibility};
 use Type::*;
 
 use crate::context::initialize::*;
@@ -108,14 +108,14 @@ impl Context {
             poly(ENUMERATE, vec![ty_tp(T.clone())]),
         )
         .quantify();
-        let guard = Type::Guard(GuardType::new(
+        let grd = guard(
             "<builtins>".into(),
             CastTarget::arg(0, "x".into(), Location::Unknown),
             U.clone(),
-        ));
+        );
         let t_filter = nd_func(
             vec![
-                kw(KW_FUNC, nd_func(vec![kw("x", T.clone())], None, guard)),
+                kw(KW_FUNC, nd_func(vec![kw("x", T.clone())], None, grd)),
                 kw(KW_ITERABLE, poly(ITERABLE, vec![ty_tp(T.clone())])),
             ],
             None,
diff --git a/crates/erg_compiler/context/initialize/traits.rs b/crates/erg_compiler/context/initialize/traits.rs
index 23f1cf094..fd2b6fe35 100644
--- a/crates/erg_compiler/context/initialize/traits.rs
+++ b/crates/erg_compiler/context/initialize/traits.rs
@@ -3,7 +3,7 @@ use erg_common::log;
 
 use crate::ty::constructors::*;
 use crate::ty::value::ValueObj;
-use crate::ty::{Type, Visibility};
+use crate::ty::{CastTarget, Type, Visibility};
 use ParamSpec as PS;
 use Type::*;
 
@@ -249,12 +249,23 @@ impl Context {
             Visibility::BUILTIN_PUBLIC,
             Some("Function::iterable_map"),
         );
+        let grd = guard(
+            "<builtins>".into(),
+            CastTarget::arg(0, "x".into(), Location::Unknown),
+            U.clone(),
+        );
         let t_filter = fn1_met(
             Slf.clone(),
-            func1(T.clone(), Bool),
-            poly(FILTER, vec![ty_tp(T.clone())]),
+            nd_func(vec![kw("x", T.clone())], None, grd),
+            poly(FILTER, vec![ty_tp(T.clone() & U.clone())]),
         )
-        .quantify();
+        .quantify()
+            & fn1_met(
+                Slf.clone(),
+                func1(T.clone(), Bool),
+                poly(FILTER, vec![ty_tp(T.clone())]),
+            )
+            .quantify();
         iterable.register_builtin_decl(
             FUNC_FILTER,
             t_filter,