diff --git a/crates/ra_hir/src/lib.rs b/crates/ra_hir/src/lib.rs
index 983ce99cb26..f50b922af21 100644
--- a/crates/ra_hir/src/lib.rs
+++ b/crates/ra_hir/src/lib.rs
@@ -110,16 +110,32 @@ pub struct SourceItemId {
 }
 
 /// Maps item's `SyntaxNode`s to `SourceFileItemId` and back.
-#[derive(Debug, PartialEq, Eq, Default)]
+#[derive(Debug, PartialEq, Eq)]
 pub struct SourceFileItems {
+    file_id: FileId,
     arena: Arena<SyntaxNode>,
 }
 
 impl SourceFileItems {
+    fn new(file_id: FileId) -> SourceFileItems {
+        SourceFileItems {
+            file_id,
+            arena: Arena::default(),
+        }
+    }
+
     fn alloc(&mut self, item: SyntaxNode) -> SourceFileItemId {
         self.arena.alloc(item)
     }
-    pub fn id_of(&self, item: SyntaxNodeRef) -> SourceFileItemId {
+    pub fn id_of(&self, file_id: FileId, item: SyntaxNodeRef) -> SourceFileItemId {
+        assert_eq!(
+            self.file_id, file_id,
+            "SourceFileItems: wrong file, expected {:?}, got {:?}",
+            self.file_id, file_id
+        );
+        self.id_of_unchecked(item)
+    }
+    fn id_of_unchecked(&self, item: SyntaxNodeRef) -> SourceFileItemId {
         let (id, _item) = self
             .arena
             .iter()
diff --git a/crates/ra_hir/src/module.rs b/crates/ra_hir/src/module.rs
index 580c737c300..e7a49f83abe 100644
--- a/crates/ra_hir/src/module.rs
+++ b/crates/ra_hir/src/module.rs
@@ -280,7 +280,7 @@ pub(crate) fn new_inline(
     ) -> ModuleSource {
         assert!(!m.has_semi());
         let file_items = db.file_items(file_id);
-        let item_id = file_items.id_of(m.syntax());
+        let item_id = file_items.id_of(file_id, m.syntax());
         ModuleSource::new(file_id, item_id)
     }
 
diff --git a/crates/ra_hir/src/module/nameres.rs b/crates/ra_hir/src/module/nameres.rs
index 61a1acfe6f9..6511359d08b 100644
--- a/crates/ra_hir/src/module/nameres.rs
+++ b/crates/ra_hir/src/module/nameres.rs
@@ -168,7 +168,7 @@ fn add_item(&mut self, file_items: &SourceFileItems, item: ast::ModuleItem) -> O
     }
 
     fn add_use_item(&mut self, file_items: &SourceFileItems, item: ast::UseItem) {
-        let file_item_id = file_items.id_of(item.syntax());
+        let file_item_id = file_items.id_of_unchecked(item.syntax());
         let start_offset = item.syntax().range().start();
         Path::expand_use_item(item, |path, range| {
             let kind = match range {
@@ -188,7 +188,7 @@ fn new<'a>(file_items: &SourceFileItems, item: impl ast::NameOwner<'a>) -> Optio
         let name = item.name()?.text();
         let kind = item.syntax().kind();
         let vis = Vis::Other;
-        let id = file_items.id_of(item.syntax());
+        let id = file_items.id_of_unchecked(item.syntax());
         let res = ModuleItem {
             id,
             name,
diff --git a/crates/ra_hir/src/query_definitions.rs b/crates/ra_hir/src/query_definitions.rs
index e4d721601df..bb4457d072e 100644
--- a/crates/ra_hir/src/query_definitions.rs
+++ b/crates/ra_hir/src/query_definitions.rs
@@ -36,7 +36,7 @@ pub(super) fn fn_scopes(db: &impl HirDatabase, fn_id: FnId) -> Arc<FnScopes> {
 }
 
 pub(super) fn file_items(db: &impl HirDatabase, file_id: FileId) -> Arc<SourceFileItems> {
-    let mut res = SourceFileItems::default();
+    let mut res = SourceFileItems::new(file_id);
     let source_file = db.source_file(file_id);
     res.alloc(source_file.syntax().owned());
     let source_file = source_file.borrowed();
diff --git a/crates/ra_hir/src/source_binder.rs b/crates/ra_hir/src/source_binder.rs
index 47915580502..0c16ccc243d 100644
--- a/crates/ra_hir/src/source_binder.rs
+++ b/crates/ra_hir/src/source_binder.rs
@@ -75,7 +75,7 @@ pub fn function_from_source(
 ) -> Cancelable<Option<Function>> {
     let module = ctry!(module_from_child_node(db, file_id, fn_def.syntax())?);
     let file_items = db.file_items(file_id);
-    let item_id = file_items.id_of(fn_def.syntax());
+    let item_id = file_items.id_of(file_id, fn_def.syntax());
     let source_item_id = SourceItemId { file_id, item_id };
     let def_loc = DefLoc {
         kind: DefKind::Function,