diff --git a/compiler/rustc_metadata/src/rmeta/decoder.rs b/compiler/rustc_metadata/src/rmeta/decoder.rs
index 706f3f6d8542b..59fec58f0a1b3 100644
--- a/compiler/rustc_metadata/src/rmeta/decoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/decoder.rs
@@ -1931,6 +1931,10 @@ impl CrateMetadata {
         self.root.hash
     }
 
+    fn num_def_ids(&self) -> usize {
+        self.root.tables.def_keys.size()
+    }
+
     fn local_def_id(&self, index: DefIndex) -> DefId {
         DefId { krate: self.cnum, index }
     }
diff --git a/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs b/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
index 02d1cf9aec79f..dfa82b6c046d5 100644
--- a/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
+++ b/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
@@ -454,6 +454,13 @@ impl CStore {
         self.get_crate_data(def_id.krate).module_expansion(def_id.index, sess)
     }
 
+    /// Only public-facing way to traverse all the definitions in a non-local crate.
+    /// Critically useful for this third-party project: https://github.com/hacspec/hacspec.
+    /// See https://github.com/rust-lang/rust/pull/85889 for context.
+    pub fn num_def_ids_untracked(&self, cnum: CrateNum) -> usize {
+        self.get_crate_data(cnum).num_def_ids()
+    }
+
     pub fn item_attrs(&self, def_id: DefId, sess: &Session) -> Vec<ast::Attribute> {
         self.get_crate_data(def_id.krate).get_item_attrs(def_id.index, sess).collect()
     }