diff --git a/crates/oxc_ast/src/ast/js.rs b/crates/oxc_ast/src/ast/js.rs
index 4ba636208..c7ff4df6e 100644
--- a/crates/oxc_ast/src/ast/js.rs
+++ b/crates/oxc_ast/src/ast/js.rs
@@ -1175,9 +1175,8 @@ pub struct DebuggerStatement {
 
 /// Destructuring Binding Patterns
 #[derive(Debug, Hash)]
-#[cfg_attr(feature = "serde", derive(Serialize), serde(rename_all = "camelCase"))]
+#[cfg_attr(feature = "serde", derive(Serialize), serde(tag = "type", rename_all = "camelCase"))]
 pub struct BindingPattern<'a> {
-    #[cfg_attr(feature = "serde", serde(flatten))]
     pub kind: BindingPatternKind<'a>,
     pub type_annotation: Option<Box<'a, TSTypeAnnotation<'a>>>,
     pub optional: bool,
@@ -1309,11 +1308,10 @@ pub struct FormalParameters<'a> {
 }
 
 #[derive(Debug, Hash)]
-#[cfg_attr(feature = "serde", derive(Serialize))]
+#[cfg_attr(feature = "serde", derive(Serialize), serde(tag = "type"))]
 pub struct FormalParameter<'a> {
     #[cfg_attr(feature = "serde", serde(flatten))]
     pub span: Span,
-    #[cfg_attr(feature = "serde", serde(flatten))]
     pub pattern: BindingPattern<'a>,
     pub accessibility: Option<TSAccessibility>,
     pub readonly: bool,
@@ -1321,7 +1319,7 @@ pub struct FormalParameter<'a> {
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
-#[cfg_attr(feature = "serde", derive(Serialize), serde(untagged))]
+#[cfg_attr(feature = "serde", derive(Serialize))]
 pub enum FormalParameterKind {
     /// <https://tc39.es/ecma262/#prod-FormalParameters>
     FormalParameter,
diff --git a/crates/oxc_hir/src/hir.rs b/crates/oxc_hir/src/hir.rs
index d1cd6e4b3..7af82b05a 100644
--- a/crates/oxc_hir/src/hir.rs
+++ b/crates/oxc_hir/src/hir.rs
@@ -1382,17 +1382,16 @@ pub struct FormalParameters<'a> {
 }
 
 #[derive(Debug, Hash)]
-#[cfg_attr(feature = "serde", derive(Serialize))]
+#[cfg_attr(feature = "serde", derive(Serialize), serde(tag = "type"))]
 pub struct FormalParameter<'a> {
     #[cfg_attr(feature = "serde", serde(flatten))]
     pub span: Span,
-    #[cfg_attr(feature = "serde", serde(flatten))]
     pub pattern: BindingPattern<'a>,
     pub decorators: Vec<'a, Decorator<'a>>,
 }
 
 #[derive(Debug, Clone, Copy, Hash)]
-#[cfg_attr(feature = "serde", derive(Serialize), serde(untagged))]
+#[cfg_attr(feature = "serde", derive(Serialize))]
 pub enum FormalParameterKind {
     /// <https://tc39.es/ecma262/#prod-FormalParameters>
     FormalParameter,