diff --git a/third_party/java/src/io/netty_voltpatches/NinjaKeySet.java b/third_party/java/src/io/netty_voltpatches/NinjaKeySet.java
index <HASH>..<HASH> 100644
--- a/third_party/java/src/io/netty_voltpatches/NinjaKeySet.java
+++ b/third_party/java/src/io/netty_voltpatches/NinjaKeySet.java
@@ -98,7 +98,7 @@ public final class NinjaKeySet extends AbstractSet<SelectionKey> {
 
             // Ensure the current selector implementation is what we can instrument.
             if (!selectorImplClass.isAssignableFrom(selector.getClass())) {
-                return selectedKeySet;
+                return null;
             }
 
             Field selectedKeysField = selectorImplClass.getDeclaredField("selectedKeys");
For ENG-<I>, fix bug where null isn't return for incompatible selectors