diff --git a/src/types.ts b/src/types.ts
index 8b65e6f42..7a13fab6b 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -154,7 +154,7 @@ export type RequestInterface = OctokitTypes.RequestInterface;
 export type Cache =
   | Lru<string>
   | {
-      get: (key: string) => string | Promise<string>;
+      get: (key: string) => string | Promise<string | null | undefined>;
       set: (key: string, value: string) => any;
     };