diff --git a/crates/ra_hir/src/lib.rs b/crates/ra_hir/src/lib.rs
index ca261e8f54..227e931833 100644
--- a/crates/ra_hir/src/lib.rs
+++ b/crates/ra_hir/src/lib.rs
@@ -80,7 +80,7 @@ pub use self::{
     path::{Path, PathKind},
     resolve::ScopeDef,
     source_binder::{PathResolution, ScopeEntryWithSyntax, SourceAnalyzer},
-    source_id::{AstIdMap, ErasedFileAstId},
+    source_id::AstIdMap,
     ty::{
         display::HirDisplay, ApplicationTy, CallableDef, Substs, TraitRef, Ty, TypeCtor, TypeWalk,
     },
diff --git a/crates/ra_hir/src/source_id.rs b/crates/ra_hir/src/source_id.rs
index c69a2afeb6..463b1d4535 100644
--- a/crates/ra_hir/src/source_id.rs
+++ b/crates/ra_hir/src/source_id.rs
@@ -1,6 +1,6 @@
 //! FIXME: write short doc here
 
 pub use hir_expand::{
-    ast_id_map::{AstIdMap, ErasedFileAstId, FileAstId},
+    ast_id_map::{AstIdMap, FileAstId},
     AstId,
 };
diff --git a/crates/ra_hir_expand/src/ast_id_map.rs b/crates/ra_hir_expand/src/ast_id_map.rs
index 2f43abe152..919ede0a03 100644
--- a/crates/ra_hir_expand/src/ast_id_map.rs
+++ b/crates/ra_hir_expand/src/ast_id_map.rs
@@ -8,11 +8,10 @@
 use std::{
     hash::{Hash, Hasher},
     marker::PhantomData,
-    ops,
 };
 
 use ra_arena::{impl_arena_id, Arena, RawId};
-use ra_syntax::{ast, AstNode, SyntaxNode, SyntaxNodePtr};
+use ra_syntax::{ast, AstNode, AstPtr, SyntaxNode, SyntaxNodePtr};
 
 /// `AstId` points to an AST node in a specific file.
 #[derive(Debug)]
@@ -40,14 +39,8 @@ impl<N: AstNode> Hash for FileAstId<N> {
     }
 }
 
-impl<N: AstNode> From<FileAstId<N>> for ErasedFileAstId {
-    fn from(id: FileAstId<N>) -> Self {
-        id.raw
-    }
-}
-
 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
-pub struct ErasedFileAstId(RawId);
+struct ErasedFileAstId(RawId);
 impl_arena_id!(ErasedFileAstId);
 
 /// Maps items' `SyntaxNode`s to `ErasedFileAstId`s and back.
@@ -90,18 +83,15 @@ impl AstIdMap {
         }
     }
 
+    pub fn get<N: AstNode>(&self, id: FileAstId<N>) -> AstPtr<N> {
+        self.arena[id.raw].cast::<N>().unwrap()
+    }
+
     fn alloc(&mut self, item: &SyntaxNode) -> ErasedFileAstId {
         self.arena.alloc(SyntaxNodePtr::new(item))
     }
 }
 
-impl ops::Index<ErasedFileAstId> for AstIdMap {
-    type Output = SyntaxNodePtr;
-    fn index(&self, index: ErasedFileAstId) -> &SyntaxNodePtr {
-        &self.arena[index]
-    }
-}
-
 /// Walks the subtree in bfs order, calling `f` for each node.
 fn bfs(node: &SyntaxNode, mut f: impl FnMut(SyntaxNode)) {
     let mut curr_layer = vec![node.clone()];
diff --git a/crates/ra_hir_expand/src/lib.rs b/crates/ra_hir_expand/src/lib.rs
index 1fb1243741..a31b9fa4cd 100644
--- a/crates/ra_hir_expand/src/lib.rs
+++ b/crates/ra_hir_expand/src/lib.rs
@@ -172,7 +172,6 @@ impl<N: AstNode> AstId<N> {
 
     pub fn to_node(&self, db: &impl AstDatabase) -> N {
         let root = db.parse_or_expand(self.file_id).unwrap();
-        let node = db.ast_id_map(self.file_id)[self.file_ast_id.into()].to_node(&root);
-        N::cast(node).unwrap()
+        db.ast_id_map(self.file_id).get(self.file_ast_id).to_node(&root)
     }
 }