diff --git a/types/index.d.ts b/types/index.d.ts
index 551e742..fdc372c 100644
--- a/types/index.d.ts
+++ b/types/index.d.ts
@@ -21,7 +21,7 @@ declare class OrderedMap<T = any> {
 
   subtract(map: MapLike<T>): OrderedMap<T>
 
-  get size(): number
+  readonly size: number
 
   static from<T>(map: MapLike<T>): OrderedMap<T>
 }