diff --git a/compiler/erg_compiler/context/instantiate.rs b/compiler/erg_compiler/context/instantiate.rs
index c1561fbc..8ad73b62 100644
--- a/compiler/erg_compiler/context/instantiate.rs
+++ b/compiler/erg_compiler/context/instantiate.rs
@@ -767,14 +767,23 @@ impl Context {
         &self,
         p: &ParamTySpec,
         opt_decl_t: Option<&ParamTy>,
+        default_t: Option<&TypeSpec>,
         tmp_tv_ctx: Option<&TyVarInstContext>,
         mode: RegistrationMode,
     ) -> TyCheckResult<ParamTy> {
         let t = self.instantiate_typespec(&p.ty, opt_decl_t, tmp_tv_ctx, mode)?;
-        Ok(ParamTy::pos(
-            p.name.as_ref().map(|t| t.inspect().to_owned()),
-            t,
-        ))
+        if let Some(default_t) = default_t {
+            Ok(ParamTy::kw_default(
+                p.name.as_ref().unwrap().inspect().to_owned(),
+                t,
+                self.instantiate_typespec(default_t, opt_decl_t, tmp_tv_ctx, mode)?,
+            ))
+        } else {
+            Ok(ParamTy::pos(
+                p.name.as_ref().map(|t| t.inspect().to_owned()),
+                t,
+            ))
+        }
     }
 
     pub(crate) fn instantiate_typespec(
@@ -854,15 +863,23 @@ impl Context {
             }
             TypeSpec::Subr(subr) => {
                 let non_defaults = try_map_mut(subr.non_defaults.iter(), |p| {
-                    self.instantiate_func_param_spec(p, opt_decl_t, tmp_tv_ctx, mode)
+                    self.instantiate_func_param_spec(p, opt_decl_t, None, tmp_tv_ctx, mode)
                 })?;
                 let var_args = subr
                     .var_args
                     .as_ref()
-                    .map(|p| self.instantiate_func_param_spec(p, opt_decl_t, tmp_tv_ctx, mode))
+                    .map(|p| {
+                        self.instantiate_func_param_spec(p, opt_decl_t, None, tmp_tv_ctx, mode)
+                    })
                     .transpose()?;
                 let defaults = try_map_mut(subr.defaults.iter(), |p| {
-                    self.instantiate_func_param_spec(p, opt_decl_t, tmp_tv_ctx, mode)
+                    self.instantiate_func_param_spec(
+                        &p.param,
+                        opt_decl_t,
+                        Some(&p.default),
+                        tmp_tv_ctx,
+                        mode,
+                    )
                 })?
                 .into_iter()
                 .collect();
diff --git a/compiler/erg_parser/ast.rs b/compiler/erg_parser/ast.rs
index ffd4dc1f..fd3ed429 100644
--- a/compiler/erg_parser/ast.rs
+++ b/compiler/erg_parser/ast.rs
@@ -1591,13 +1591,31 @@ impl ParamTySpec {
     }
 }
 
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub struct DefaultParamTySpec {
+    pub param: ParamTySpec,
+    pub default: TypeSpec,
+}
+
+impl fmt::Display for DefaultParamTySpec {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{} := {}", self.param, self.default)
+    }
+}
+
+impl DefaultParamTySpec {
+    pub const fn new(param: ParamTySpec, default: TypeSpec) -> Self {
+        Self { param, default }
+    }
+}
+
 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
 pub struct SubrTypeSpec {
     pub bounds: TypeBoundSpecs,
     pub lparen: Option<Token>,
     pub non_defaults: Vec<ParamTySpec>,
     pub var_args: Option<Box<ParamTySpec>>,
-    pub defaults: Vec<ParamTySpec>,
+    pub defaults: Vec<DefaultParamTySpec>,
     pub arrow: Token,
     pub return_t: Box<TypeSpec>,
 }
@@ -1638,7 +1656,7 @@ impl SubrTypeSpec {
         lparen: Option<Token>,
         non_defaults: Vec<ParamTySpec>,
         var_args: Option<ParamTySpec>,
-        defaults: Vec<ParamTySpec>,
+        defaults: Vec<DefaultParamTySpec>,
         arrow: Token,
         return_t: TypeSpec,
     ) -> Self {
diff --git a/compiler/erg_parser/parse.rs b/compiler/erg_parser/parse.rs
index a2517c61..06349ca4 100644
--- a/compiler/erg_parser/parse.rs
+++ b/compiler/erg_parser/parse.rs
@@ -2813,12 +2813,18 @@ impl Parser {
         for param in lambda.sig.params.defaults.into_iter() {
             let param = match (param.sig.pat, param.sig.t_spec) {
                 (ParamPattern::VarName(name), Some(t_spec_with_op)) => {
-                    ParamTySpec::new(Some(name.into_token()), t_spec_with_op.t_spec)
+                    let param_spec =
+                        ParamTySpec::new(Some(name.into_token()), t_spec_with_op.t_spec);
+                    let default_spec = Self::expr_to_type_spec(param.default_val)?;
+                    DefaultParamTySpec::new(param_spec, default_spec)
                 }
-                (ParamPattern::VarName(name), None) => ParamTySpec::anonymous(TypeSpec::PreDeclTy(
-                    PreDeclTypeSpec::Simple(SimpleTypeSpec::new(name, ConstArgs::empty())),
-                )),
-                _ => todo!(),
+                (ParamPattern::VarName(name), None) => {
+                    let default_spec = Self::expr_to_type_spec(param.default_val)?;
+                    let param_spec =
+                        ParamTySpec::new(Some(name.into_token()), default_spec.clone());
+                    DefaultParamTySpec::new(param_spec, default_spec)
+                }
+                (l, r) => todo!("{:?} {:?}", l, r),
             };
             defaults.push(param);
         }