diff --git a/crates/ra_hir/src/code_model.rs b/crates/ra_hir/src/code_model.rs
index 3936f5aaa05e..cdbf475b3641 100644
--- a/crates/ra_hir/src/code_model.rs
+++ b/crates/ra_hir/src/code_model.rs
@@ -992,8 +992,8 @@ impl TypeParam {
 
     pub fn default(self, db: &dyn HirDatabase) -> Option<Ty> {
         let params = db.generic_defaults(self.id.parent);
-        let local_idx: u32 = self.id.local_id.into_raw().into();
-        params.get(local_idx as usize).map(|d| d.clone())
+        let local_idx = hir_ty::param_idx(db, self.id)?;
+        params.get(local_idx).map(|d| d.clone())
     }
 }
 
diff --git a/crates/ra_hir_ty/src/lib.rs b/crates/ra_hir_ty/src/lib.rs
index e8f3482fe463..ccc4348f4269 100644
--- a/crates/ra_hir_ty/src/lib.rs
+++ b/crates/ra_hir_ty/src/lib.rs
@@ -427,6 +427,11 @@ impl Substs {
     }
 }
 
+/// Return an index of a parameter in the generic type parameter list by it's id.
+pub fn param_idx(db: &dyn HirDatabase, id: TypeParamId) -> Option<usize> {
+    generics(db.upcast(), id.parent).param_idx(id)
+}
+
 #[derive(Debug, Clone)]
 pub struct SubstsBuilder {
     vec: Vec<Ty>,