diff --git a/compiler/rustc_ast_lowering/src/delegation/resolution.rs b/compiler/rustc_ast_lowering/src/delegation/resolution.rs
index 7678418c47e56..8e35b05d7e870 100644
--- a/compiler/rustc_ast_lowering/src/delegation/resolution.rs
+++ b/compiler/rustc_ast_lowering/src/delegation/resolution.rs
@@ -4,7 +4,6 @@ use ast::visit::Visitor;
 use hir::def::DefKind;
 use rustc_ast::{self as ast, AssocItemKind, Delegation, DelegationSource, Item, ItemKind, NodeId};
 use rustc_data_structures::fx::{FxHashSet, FxIndexMap, FxIndexSet};
-use rustc_data_structures::steal::Steal;
 use rustc_hir as hir;
 use rustc_middle::middle::resolve::{
     self as mid_res, AstOwner, DelegationInherentFnKind, TypeRelativeDelegationRes,
@@ -53,9 +52,10 @@ pub(crate) fn resolve_type_relative_delegations(
             // Also record resolutions for cases when signature is resolved but call path is not.
             mid_res::DelegationResolution::Partial
             | mid_res::DelegationResolution::PartialCall(_) => {
-                let Some(r_and_owner) = ast_index.get(def_id).map(Steal::borrow) else {
-                    unreachable!("ast index must contain delegations");
-                };
+                let r_and_owner = ast_index[def_id]
+                    .as_ref()
+                    .expect("ast index must contain delegations")
+                    .borrow();
 
                 let (r, owner) = &*r_and_owner;
 
diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs
index b6d1017665ec6..a99db03007b51 100644
--- a/compiler/rustc_ast_lowering/src/lib.rs
+++ b/compiler/rustc_ast_lowering/src/lib.rs
@@ -587,7 +587,7 @@ enum TryBlockScope {
 fn index_ast<'tcx>(
     tcx: TyCtxt<'tcx>,
     (): (),
-) -> &'tcx IndexSlice<LocalDefId, Steal<(Arc<ResolverAstLowering<'tcx>>, AstOwner)>> {
+) -> &'tcx IndexSlice<LocalDefId, Option<Steal<(Arc<ResolverAstLowering<'tcx>>, AstOwner)>>> {
     // Queries that borrow `resolver_for_lowering`.
     tcx.ensure_done().output_filenames(());
     tcx.ensure_done().early_lint_checks(());
@@ -610,20 +610,19 @@ fn index_ast<'tcx>(
     let index = indexer.index;
     let resolver = Arc::new(resolver);
     return tcx.arena.alloc_index_slice_from_iter::<LocalDefId, _, _>(
-        index.into_iter().map(|owner| Steal::new((Arc::clone(&resolver), owner))),
+        index.into_iter().map(|owner| owner.map(|o| Steal::new((Arc::clone(&resolver), o)))),
     );
 
     struct Indexer<'s, 'hir> {
         owners: &'s NodeMap<PerOwnerResolverData<'hir>>,
-        index: IndexVec<LocalDefId, AstOwner>,
+        index: IndexVec<LocalDefId, Option<AstOwner>>,
         next_node_id: NodeId,
     }
 
     impl Indexer<'_, '_> {
         fn insert(&mut self, id: NodeId, node: AstOwner) {
             let def_id = self.owners[&id].def_id;
-            self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner);
-            self.index[def_id] = node;
+            self.index.insert(def_id, node);
         }
 
         fn make_dummy<K>(
@@ -705,7 +704,7 @@ fn lower_to_hir(tcx: TyCtxt<'_>, def_id: LocalDefId) -> hir::MaybeOwner<'_> {
     tcx.ensure_done().resolve_type_relative_delegations(());
 
     let ast_index = tcx.index_ast(());
-    let resolver_and_node = ast_index.get(def_id).map(Steal::steal);
+    let resolver_and_node = ast_index.get(def_id);
 
     let fallback_to_ancestor = || {
         // The item did not exist in the AST, it was created while lowering another item.
@@ -732,10 +731,13 @@ fn lower_to_hir(tcx: TyCtxt<'_>, def_id: LocalDefId) -> hir::MaybeOwner<'_> {
         })
     };
 
-    let Some((resolver, node)) = resolver_and_node else {
+    let Some(Some(r_and_node)) = resolver_and_node else {
         // `ast_index` does not contain all definitions, only up-to the highest
         // `LocalDefId` which has a non-trivial `AstOwner`. Gracefully handle
         // other definitions, in particular those nested inside this highest definition.
+        // OR
+        // The item existed in the AST, but is not a HIR owner.
+        // Fetch the correct information from its parent.
         return fallback_to_ancestor();
     };
 
@@ -750,6 +752,8 @@ fn lower_to_hir(tcx: TyCtxt<'_>, def_id: LocalDefId) -> hir::MaybeOwner<'_> {
         hir::MaybeOwner::Owner(lctx.curr_owner.into_owner_info(tcx, item))
     }
 
+    let (resolver, node) = r_and_node.steal();
+
     let item = match &node {
         // The item existed in the AST.
         AstOwner::Crate(c) => with_lctx(tcx, &*resolver, CRATE_NODE_ID, |lctx| {
@@ -770,9 +774,6 @@ fn lower_to_hir(tcx: TyCtxt<'_>, def_id: LocalDefId) -> hir::MaybeOwner<'_> {
         AstOwner::ForeignItem(item) => with_lctx(tcx, &*resolver, item.id, |lctx| {
             hir::OwnerNode::ForeignItem(lctx.lower_foreign_item(item))
         }),
-        // The item existed in the AST, but is not a HIR owner.
-        // Fetch the correct information from its parent.
-        AstOwner::NonOwner => fallback_to_ancestor(),
     };
 
     tcx.sess.time("drop_ast", || mem::drop(node));
diff --git a/compiler/rustc_middle/src/arena.rs b/compiler/rustc_middle/src/arena.rs
index a423b6bdca5b2..d2e6c4bbe2466 100644
--- a/compiler/rustc_middle/src/arena.rs
+++ b/compiler/rustc_middle/src/arena.rs
@@ -43,10 +43,10 @@ rustc_arena::declare_arena! {
             rustc_middle::middle::resolve::ResolverAstLowering<'tcx>
         >,
     index_ast:
-        rustc_data_structures::steal::Steal<(
+        Option<rustc_data_structures::steal::Steal<(
             std::sync::Arc<rustc_middle::middle::resolve::ResolverAstLowering<'tcx>>,
             rustc_middle::middle::resolve::AstOwner
-        )>,
+        )>>,
     crate_alone: rustc_data_structures::steal::Steal<rustc_ast::Crate>,
     crate_for_resolver: rustc_data_structures::steal::Steal<(rustc_ast::Crate, rustc_ast::AttrVec)>,
     resolutions: rustc_middle::middle::resolve::ResolverGlobalCtxt,
diff --git a/compiler/rustc_middle/src/middle/resolve.rs b/compiler/rustc_middle/src/middle/resolve.rs
index bafb45469a56e..013edbf24739a 100644
--- a/compiler/rustc_middle/src/middle/resolve.rs
+++ b/compiler/rustc_middle/src/middle/resolve.rs
@@ -332,8 +332,6 @@ pub type DocLinkResMap = FxIndexMap<(Symbol, Namespace), Option<Res<NodeId>>>;
 /// is as good a place as any for it.
 #[derive(Debug)]
 pub enum AstOwner {
-    /// This definition does not correspond to a HIR owner.
-    NonOwner,
     Crate(Box<ast::Crate>),
     Item(Box<ast::Item>),
     TraitItem(Box<ast::AssocItem>),
diff --git a/compiler/rustc_middle/src/queries.rs b/compiler/rustc_middle/src/queries.rs
index d9d618519446d..d0429df43d1dd 100644
--- a/compiler/rustc_middle/src/queries.rs
+++ b/compiler/rustc_middle/src/queries.rs
@@ -206,13 +206,11 @@ rustc_queries! {
         desc { "getting the resolver for lowering" }
     }
 
-    query index_ast(_: ()) -> &'tcx IndexSlice<LocalDefId, Steal<(
-        // There is only a single `ResolverAstLowering` for all owners.
-        // We want to drop it once the whole HIR has been lowered.
-        // We rely on reference counting to know when all definitions have been stolen.
-        Arc<ResolverAstLowering<'tcx>>,
-        AstOwner,
-    )>> {
+    // There is only a single `ResolverAstLowering` for all owners.
+    // We want to drop it once the whole HIR has been lowered.
+    // We rely on reference counting to know when all definitions have been stolen.
+    // None if the `LocalDefId` is not an owner.
+    query index_ast(_: ()) -> &'tcx IndexSlice<LocalDefId, Option<Steal<(Arc<ResolverAstLowering<'tcx>>, AstOwner)>>>  {
         eval_always
         no_hash
         desc { "getting the AST for lowering" }