diff --git a/x-pack/plugin/blob-cache/src/main/java/org/elasticsearch/blobcache/shared/SharedBlobCacheService.java b/x-pack/plugin/blob-cache/src/main/java/org/elasticsearch/blobcache/shared/SharedBlobCacheService.java
index 453aa792a5da5..68a13125eba3d 100644
--- a/x-pack/plugin/blob-cache/src/main/java/org/elasticsearch/blobcache/shared/SharedBlobCacheService.java
+++ b/x-pack/plugin/blob-cache/src/main/java/org/elasticsearch/blobcache/shared/SharedBlobCacheService.java
@@ -1415,6 +1415,7 @@ private SharedBytes.IO maybeEvictAndTake(Runnable evictedNotification) {
                             if (ioRef != null) {
                                 try {
                                     if (entry.chunk.refCount() == 1) {
+                                        // we own that one refcount (since we CAS'ed evicted to 1)
                                         // grab io, rely on incref'ers also checking evicted field.
                                         entry.chunk.io = null;
                                         assert regionOwners.remove(ioRef) == entry.chunk;