diff --git a/shiroha-server/src/main/java/io/nanachiyo0721/shiroha/data/BufferedLinearRegionFile.java b/shiroha-server/src/main/java/io/nanachiyo0721/shiroha/data/BufferedLinearRegionFile.java
index 45b390d..5decea6 100644
--- a/shiroha-server/src/main/java/io/nanachiyo0721/shiroha/data/BufferedLinearRegionFile.java
+++ b/shiroha-server/src/main/java/io/nanachiyo0721/shiroha/data/BufferedLinearRegionFile.java
@@ -1417,7 +1417,7 @@ public class BufferedLinearRegionFile implements io.nanachiyo0721.shiroha.data.R
             }
         }
 
-        private void markBucketsSynced(long[] syncedBucketEpochs) {
+        private void markBucketsSynced(long @NonNull [] syncedBucketEpochs) {
             for (int i = 0; i < syncedBucketEpochs.length; i++) {
                 // note: a dirty bucket always has a write epoch >= 1, so 0 = untouched
                 if (syncedBucketEpochs[i] != 0L) {