diff --git a/src/test/mock_storage.rs b/src/test/mock_storage.rs
index 5daa12838..48907a67b 100644
--- a/src/test/mock_storage.rs
+++ b/src/test/mock_storage.rs
@@ -65,7 +65,7 @@ impl Storage for MockStorage {
             Duration::from_secs(0)
         })
     }
-    async fn timestamp_cache_hit(&self, _key: &str) -> Result<Duration> {
+    async fn timestamp_cache_hit(&self, _key: &str) -> Result<Option<Duration>> {
         Ok(Duration::from_secs(0))
     }
     fn location(&self) -> String {