diff --git a/artio-core/src/main/java/uk/co/real_logic/artio/engine/framer/NioSelectedKeySet.java b/artio-core/src/main/java/uk/co/real_logic/artio/engine/framer/NioSelectedKeySet.java
index fb48b93814..805f6ecad2 100644
--- a/artio-core/src/main/java/uk/co/real_logic/artio/engine/framer/NioSelectedKeySet.java
+++ b/artio-core/src/main/java/uk/co/real_logic/artio/engine/framer/NioSelectedKeySet.java
@@ -27,7 +27,7 @@
  * Try to fix handling of HashSet for {@link java.nio.channels.Selector} to avoid excessive allocation.
  * Assumes single threaded usage.
  */
-public class NioSelectedKeySet extends AbstractSet<SelectionKey>
+final class NioSelectedKeySet extends AbstractSet<SelectionKey>
 {
     private static final int INITIAL_CAPACITY = 10;