diff --git a/src/cache.ts b/src/cache.ts
index 242e1ed..d808722 100644
--- a/src/cache.ts
+++ b/src/cache.ts
@@ -6,7 +6,7 @@ export interface ICacheOptions {
 }
 
 export interface ICachePolicy {
-    maxEntries: number;
+    maxEntries?: number;
     stdTTL: number; // second
 }