diff --git a/processing/src/main/java/io/druid/query/aggregation/cardinality/CardinalityAggregatorFactory.java b/processing/src/main/java/io/druid/query/aggregation/cardinality/CardinalityAggregatorFactory.java
index 071a91b3c3e..368ebbc6f2d 100644
--- a/processing/src/main/java/io/druid/query/aggregation/cardinality/CardinalityAggregatorFactory.java
+++ b/processing/src/main/java/io/druid/query/aggregation/cardinality/CardinalityAggregatorFactory.java
@@ -214,9 +214,10 @@ public class CardinalityAggregatorFactory implements AggregatorFactory
   {
     byte[] fieldNameBytes = Joiner.on("\u0001").join(fieldNames).getBytes(Charsets.UTF_8);
 
-    return ByteBuffer.allocate(1 + fieldNameBytes.length)
+    return ByteBuffer.allocate(2 + fieldNameBytes.length)
                      .put(CACHE_TYPE_ID)
                      .put(fieldNameBytes)
+                     .put((byte)(byRow ? 1 : 0))
                      .array();
   }