diff --git a/specification/storage/data-plane/Microsoft.BlobStorage/preview/2019-12-12/blob.json b/specification/storage/data-plane/Microsoft.BlobStorage/preview/2019-12-12/blob.json
index 4ed0358e2c7d..c30f63bbe26c 100644
--- a/specification/storage/data-plane/Microsoft.BlobStorage/preview/2019-12-12/blob.json
+++ b/specification/storage/data-plane/Microsoft.BlobStorage/preview/2019-12-12/blob.json
@@ -9090,7 +9090,8 @@
         },
         "Size": {
           "description": "The block size in bytes.",
-          "type": "integer"
+          "type": "integer",
+          "format": "int64"
         }
       }
     },