diff --git a/crates/hir-def/src/expr_store/tests/body/block.rs b/crates/hir-def/src/expr_store/tests/body/block.rs
index 71fcced2d85b..906c4835c795 100644
--- a/crates/hir-def/src/expr_store/tests/body/block.rs
+++ b/crates/hir-def/src/expr_store/tests/body/block.rs
@@ -199,6 +199,11 @@ fn f() {
                         4401,
                     ),
                 ),
+                containing_module_inside_def_map: None,
+                name_or_empty: Name {
+                    symbol: "",
+                    ctx: (),
+                },
             }"#]],
     );
 }
diff --git a/crates/hir-def/src/lib.rs b/crates/hir-def/src/lib.rs
index 3aaf89102fab..e6bf8a2a19aa 100644
--- a/crates/hir-def/src/lib.rs
+++ b/crates/hir-def/src/lib.rs
@@ -48,7 +48,7 @@ pub mod find_path;
 pub mod import_map;
 pub mod visibility;
 
-use intern::Interned;
+use intern::{Interned, sym};
 use rustc_abi::ExternAbi;
 use thin_vec::ThinVec;
 
@@ -457,6 +457,11 @@ pub struct ModuleIdLt<'db> {
     /// `BlockId` of that block expression. If `None`, this module is part of the crate-level
     /// `DefMap` of `krate`.
     pub block: Option<BlockId>,
+    /// The parent module of this module, or `None` if this is the root module inside the def
+    /// map (including for block def maps).
+    pub containing_module_inside_def_map: Option<ModuleIdLt<'db>>,
+    /// The name of this module, or [`sym::__empty`] for the root module.
+    name_or_empty: Name,
 }
 pub type ModuleId = ModuleIdLt<'static>;
 
@@ -502,21 +507,23 @@ impl ModuleId {
     }
 
     pub fn name(self, db: &dyn DefDatabase) -> Option<Name> {
-        let def_map = self.def_map(db);
-        let parent = def_map[self].parent?;
-        def_map[parent].children.iter().find_map(|(name, module_id)| {
-            if *module_id == self { Some(name.clone()) } else { None }
-        })
+        let name = self.name_or_empty(db);
+        if *name.symbol() == sym::__empty { None } else { Some(name) }
     }
 
     /// Returns the module containing `self`, either the parent `mod`, or the module (or block) containing
     /// the block, if `self` corresponds to a block expression.
     pub fn containing_module(self, db: &dyn DefDatabase) -> Option<ModuleId> {
-        self.def_map(db).containing_module(self)
+        self.containing_module_inside_def_map(db)
+            .or_else(|| self.block(db).map(|block| block.loc(db).module))
+            .map(|module| {
+                // SAFETY: Not sure.
+                unsafe { module.to_static() }
+            })
     }
 
     pub fn is_block_module(self, db: &dyn DefDatabase) -> bool {
-        self.block(db).is_some() && self.def_map(db).root_module_id() == self
+        self.block(db).is_some() && self.containing_module_inside_def_map(db).is_none()
     }
 }
 
diff --git a/crates/hir-def/src/nameres.rs b/crates/hir-def/src/nameres.rs
index 88e3408a33b1..cf25e4cc7e07 100644
--- a/crates/hir-def/src/nameres.rs
+++ b/crates/hir-def/src/nameres.rs
@@ -66,7 +66,7 @@ use hir_expand::{
     EditionedFileId, ErasedAstId, HirFileId, InFile, MacroCallId, mod_path::ModPath, name::Name,
     proc_macro::ProcMacroKind,
 };
-use intern::Symbol;
+use intern::{Symbol, sym};
 use itertools::Itertools;
 use rustc_hash::FxHashMap;
 use span::{Edition, FileAstId, FileId, ROOT_ERASED_FILE_AST_ID};
@@ -465,7 +465,16 @@ impl DefMap {
         block: Option<BlockInfo>,
     ) -> DefMap {
         let mut modules = ModulesMap::new();
-        let root = unsafe { ModuleIdLt::new(db, krate, block.map(|it| it.block)).to_static() };
+        let root = unsafe {
+            ModuleIdLt::new(
+                db,
+                krate,
+                block.map(|it| it.block),
+                None,
+                Name::new_symbol_root(sym::__empty),
+            )
+            .to_static()
+        };
         modules.insert(root, module_data);
 
         DefMap {
diff --git a/crates/hir-def/src/nameres/collector.rs b/crates/hir-def/src/nameres/collector.rs
index 5ef51dbb2ca5..1d40f022121a 100644
--- a/crates/hir-def/src/nameres/collector.rs
+++ b/crates/hir-def/src/nameres/collector.rs
@@ -2428,6 +2428,8 @@ impl ModCollector<'_, '_> {
                 self.def_collector.db,
                 self.def_collector.def_map.krate,
                 self.def_collector.def_map.block_id(),
+                Some(self.module_id),
+                name.clone(),
             )
             .to_static()
         };