diff --git a/x-pack/plugin/blob-cache/src/main/java/org/elasticsearch/blobcache/BlobCacheMetrics.java b/x-pack/plugin/blob-cache/src/main/java/org/elasticsearch/blobcache/BlobCacheMetrics.java
index eb61a353d9b92..7ff9cf1fb9785 100644
--- a/x-pack/plugin/blob-cache/src/main/java/org/elasticsearch/blobcache/BlobCacheMetrics.java
+++ b/x-pack/plugin/blob-cache/src/main/java/org/elasticsearch/blobcache/BlobCacheMetrics.java
@@ -40,6 +40,10 @@ public enum CachePopulationReason {
          * When warming the cache
          */
         Warming,
+        /**
+         * When warming the cache as a result of an incoming request
+         */
+        OnlinePrewarming,
         /**
          * When the data we need is not in the cache
          */