diff --git a/presto-main/src/main/java/com/facebook/presto/operator/aggregation/TypedHistogram.java b/presto-main/src/main/java/com/facebook/presto/operator/aggregation/TypedHistogram.java
index <HASH>..<HASH> 100644
--- a/presto-main/src/main/java/com/facebook/presto/operator/aggregation/TypedHistogram.java
+++ b/presto-main/src/main/java/com/facebook/presto/operator/aggregation/TypedHistogram.java
@@ -41,9 +41,9 @@ public class TypedHistogram
     private int maxFill;
     private int mask;
 
-    private Type type;
+    private final Type type;
 
-    private BlockBuilder values;
+    private final BlockBuilder values;
     private IntBigArray hashPositions;
     private final LongBigArray counts;
Make fields final

They are effectively immutable, so there's no reason for them to be non-final