diff --git a/crates/hir-def/src/data.rs b/crates/hir-def/src/data.rs
index 68defa3858f..718f241cf78 100644
--- a/crates/hir-def/src/data.rs
+++ b/crates/hir-def/src/data.rs
@@ -15,9 +15,7 @@
     attr::Attrs,
     db::DefDatabase,
     expander::{Expander, Mark},
-    item_tree::{
-        self, AssocItem, FnFlags, ItemTree, ItemTreeId, MacroCall, ModItem, Param, TreeId,
-    },
+    item_tree::{self, AssocItem, FnFlags, ItemTree, ItemTreeId, MacroCall, ModItem, TreeId},
     macro_call_as_call_id, macro_id_to_def_id,
     nameres::{
         attr_resolution::ResolvedAttr,
@@ -69,7 +67,7 @@ pub(crate) fn fn_data_query(db: &dyn DefDatabase, func: FunctionId) -> Arc<Funct
         let is_varargs = enabled_params
             .clone()
             .next_back()
-            .map_or(false, |param| matches!(item_tree[param], Param::Varargs));
+            .map_or(false, |param| item_tree[param].type_ref.is_none());
 
         let mut flags = func.flags;
         if is_varargs {
@@ -105,10 +103,7 @@ pub(crate) fn fn_data_query(db: &dyn DefDatabase, func: FunctionId) -> Arc<Funct
             name: func.name.clone(),
             params: enabled_params
                 .clone()
-                .filter_map(|id| match &item_tree[id] {
-                    Param::Normal(ty) => Some(ty.clone()),
-                    Param::Varargs => None,
-                })
+                .filter_map(|id| item_tree[id].type_ref.clone())
                 .collect(),
             ret_type: func.ret_type.clone(),
             attrs: item_tree.attrs(db, krate, ModItem::from(loc.id.value).into()),
diff --git a/crates/hir-def/src/item_tree.rs b/crates/hir-def/src/item_tree.rs
index 4c812b62a46..3c4f21d5c69 100644
--- a/crates/hir-def/src/item_tree.rs
+++ b/crates/hir-def/src/item_tree.rs
@@ -613,10 +613,17 @@ pub struct Function {
     pub(crate) flags: FnFlags,
 }
 
-#[derive(Debug, Clone, Eq, PartialEq)]
-pub enum Param {
-    Normal(Interned<TypeRef>),
-    Varargs,
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Param {
+    /// This is [`None`] for varargs
+    pub type_ref: Option<Interned<TypeRef>>,
+    pub ast_id: ParamAstId,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum ParamAstId {
+    Param(FileAstId<ast::Param>),
+    SelfParam(FileAstId<ast::SelfParam>),
 }
 
 bitflags::bitflags! {
diff --git a/crates/hir-def/src/item_tree/lower.rs b/crates/hir-def/src/item_tree/lower.rs
index e4702c113b8..c0a880a64bb 100644
--- a/crates/hir-def/src/item_tree/lower.rs
+++ b/crates/hir-def/src/item_tree/lower.rs
@@ -295,8 +295,12 @@ fn lower_function(&mut self, func: &ast::Fn) -> Option<FileItemTreeId<Function>>
                         }
                     }
                 };
-                let ty = Interned::new(self_type);
-                let idx = self.data().params.alloc(Param::Normal(ty));
+                let type_ref = Interned::new(self_type);
+                let ast_id = self.source_ast_id_map.ast_id(&self_param);
+                let idx = self.data().params.alloc(Param {
+                    type_ref: Some(type_ref),
+                    ast_id: ParamAstId::SelfParam(ast_id),
+                });
                 self.add_attrs(
                     idx.into(),
                     RawAttrs::new(self.db.upcast(), &self_param, self.hygiene()),
@@ -305,11 +309,19 @@ fn lower_function(&mut self, func: &ast::Fn) -> Option<FileItemTreeId<Function>>
             }
             for param in param_list.params() {
                 let idx = match param.dotdotdot_token() {
-                    Some(_) => self.data().params.alloc(Param::Varargs),
+                    Some(_) => {
+                        let ast_id = self.source_ast_id_map.ast_id(&param);
+                        self.data()
+                            .params
+                            .alloc(Param { type_ref: None, ast_id: ParamAstId::Param(ast_id) })
+                    }
                     None => {
                         let type_ref = TypeRef::from_ast_opt(&self.body_ctx, param.ty());
                         let ty = Interned::new(type_ref);
-                        self.data().params.alloc(Param::Normal(ty))
+                        let ast_id = self.source_ast_id_map.ast_id(&param);
+                        self.data()
+                            .params
+                            .alloc(Param { type_ref: Some(ty), ast_id: ParamAstId::Param(ast_id) })
                     }
                 };
                 self.add_attrs(idx.into(), RawAttrs::new(self.db.upcast(), &param, self.hygiene()));
diff --git a/crates/hir-def/src/item_tree/pretty.rs b/crates/hir-def/src/item_tree/pretty.rs
index 417bd37c8a9..5036c2b8829 100644
--- a/crates/hir-def/src/item_tree/pretty.rs
+++ b/crates/hir-def/src/item_tree/pretty.rs
@@ -261,15 +261,15 @@ fn print_mod_item(&mut self, item: ModItem) {
                     self.indented(|this| {
                         for param in params.clone() {
                             this.print_attrs_of(param, "\n");
-                            match &this.tree[param] {
-                                Param::Normal(ty) => {
+                            match &this.tree[param].type_ref {
+                                Some(ty) => {
                                     if flags.contains(FnFlags::HAS_SELF_PARAM) {
                                         w!(this, "self: ");
                                     }
                                     this.print_type_ref(ty);
                                     wln!(this, ",");
                                 }
-                                Param::Varargs => {
+                                None => {
                                     wln!(this, "...");
                                 }
                             };
diff --git a/crates/hir-expand/src/ast_id_map.rs b/crates/hir-expand/src/ast_id_map.rs
index 1906ed15bae..40726505491 100644
--- a/crates/hir-expand/src/ast_id_map.rs
+++ b/crates/hir-expand/src/ast_id_map.rs
@@ -99,7 +99,7 @@ impl AstIdNode for
         TraitAlias,
         TypeAlias,
         Use,
-    AssocItem, BlockExpr, Variant, RecordField, TupleField, ConstArg
+    AssocItem, BlockExpr, Variant, RecordField, TupleField, ConstArg, Param, SelfParam
 }
 
 /// Maps items' `SyntaxNode`s to `ErasedFileAstId`s and back.