diff --git a/rust/candid/src/types/internal.rs b/rust/candid/src/types/internal.rs
index 5b8535b9..fe24bd95 100644
--- a/rust/candid/src/types/internal.rs
+++ b/rust/candid/src/types/internal.rs
@@ -626,9 +626,9 @@ pub fn unroll(t: &Type) -> Type {
 }
 
 thread_local! {
-    static ENV: RefCell<BTreeMap<TypeId, Type>> = RefCell::new(BTreeMap::new());
+    static ENV: RefCell<BTreeMap<TypeId, Type>> = const { RefCell::new(BTreeMap::new()) };
     // only used for TypeContainer
-    static ID: RefCell<BTreeMap<Type, TypeId>> = RefCell::new(BTreeMap::new());
+    static ID: RefCell<BTreeMap<Type, TypeId>> = const { RefCell::new(BTreeMap::new()) };
     static NAME: RefCell<TypeName> = RefCell::new(TypeName::default());
 }