diff --git a/crates/hir-def/src/body.rs b/crates/hir-def/src/body.rs
index 1d818d96267..d572d46e8b0 100644
--- a/crates/hir-def/src/body.rs
+++ b/crates/hir-def/src/body.rs
@@ -264,10 +264,10 @@ pub struct Body {
 #[derive(Default, Debug, Eq, PartialEq)]
 pub struct BodySourceMap {
     expr_map: FxHashMap<ExprSource, ExprId>,
-    expr_map_back: ArenaMap<ExprId, Result<ExprSource, SyntheticSyntax>>,
+    expr_map_back: ArenaMap<ExprId, ExprSource>,
 
     pat_map: FxHashMap<PatSource, PatId>,
-    pat_map_back: ArenaMap<PatId, Result<PatSource, SyntheticSyntax>>,
+    pat_map_back: ArenaMap<PatId, PatSource>,
 
     label_map: FxHashMap<LabelSource, LabelId>,
     label_map_back: ArenaMap<LabelId, LabelSource>,
@@ -420,7 +420,7 @@ fn index(&self, label: LabelId) -> &Label {
 // Perhaps `expr_syntax` and `expr_id`?
 impl BodySourceMap {
     pub fn expr_syntax(&self, expr: ExprId) -> Result<ExprSource, SyntheticSyntax> {
-        self.expr_map_back[expr].clone()
+        self.expr_map_back.get(expr).cloned().ok_or(SyntheticSyntax)
     }
 
     pub fn node_expr(&self, node: InFile<&ast::Expr>) -> Option<ExprId> {
@@ -434,7 +434,7 @@ pub fn node_macro_file(&self, node: InFile<&ast::MacroCall>) -> Option<HirFileId
     }
 
     pub fn pat_syntax(&self, pat: PatId) -> Result<PatSource, SyntheticSyntax> {
-        self.pat_map_back[pat].clone()
+        self.pat_map_back.get(pat).cloned().ok_or(SyntheticSyntax)
     }
 
     pub fn node_pat(&self, node: InFile<&ast::Pat>) -> Option<PatId> {
diff --git a/crates/hir-def/src/body/lower.rs b/crates/hir-def/src/body/lower.rs
index 8ebac5cb1c6..df536e09fde 100644
--- a/crates/hir-def/src/body/lower.rs
+++ b/crates/hir-def/src/body/lower.rs
@@ -24,7 +24,7 @@
 
 use crate::{
     adt::StructKind,
-    body::{Body, BodySourceMap, Expander, LabelSource, PatPtr, SyntheticSyntax},
+    body::{Body, BodySourceMap, Expander, LabelSource, PatPtr},
     body::{BodyDiagnostic, ExprSource, PatSource},
     builtin_type::{BuiltinFloat, BuiltinInt, BuiltinUint},
     db::DefDatabase,
@@ -152,19 +152,19 @@ fn ctx(&self) -> LowerCtx<'_> {
 
     fn alloc_expr(&mut self, expr: Expr, ptr: AstPtr<ast::Expr>) -> ExprId {
         let src = self.expander.to_source(ptr);
-        let id = self.make_expr(expr, Ok(src.clone()));
+        let id = self.make_expr(expr, src.clone());
         self.source_map.expr_map.insert(src, id);
         id
     }
     // desugared exprs don't have ptr, that's wrong and should be fixed
     // somehow.
     fn alloc_expr_desugared(&mut self, expr: Expr) -> ExprId {
-        self.make_expr(expr, Err(SyntheticSyntax))
+        self.body.exprs.alloc(expr)
     }
     fn missing_expr(&mut self) -> ExprId {
         self.alloc_expr_desugared(Expr::Missing)
     }
-    fn make_expr(&mut self, expr: Expr, src: Result<ExprSource, SyntheticSyntax>) -> ExprId {
+    fn make_expr(&mut self, expr: Expr, src: ExprSource) -> ExprId {
         let id = self.body.exprs.alloc(expr);
         self.source_map.expr_map_back.insert(id, src);
         id
@@ -172,14 +172,14 @@ fn make_expr(&mut self, expr: Expr, src: Result<ExprSource, SyntheticSyntax>) ->
 
     fn alloc_pat(&mut self, pat: Pat, ptr: PatPtr) -> PatId {
         let src = self.expander.to_source(ptr);
-        let id = self.make_pat(pat, Ok(src.clone()));
+        let id = self.make_pat(pat, src.clone());
         self.source_map.pat_map.insert(src, id);
         id
     }
     fn missing_pat(&mut self) -> PatId {
-        self.make_pat(Pat::Missing, Err(SyntheticSyntax))
+        self.body.pats.alloc(Pat::Missing)
     }
-    fn make_pat(&mut self, pat: Pat, src: Result<PatSource, SyntheticSyntax>) -> PatId {
+    fn make_pat(&mut self, pat: Pat, src: PatSource) -> PatId {
         let id = self.body.pats.alloc(pat);
         self.source_map.pat_map_back.insert(id, src);
         id