diff --git a/transport/src/main/java/io/netty/channel/nio/NioEventLoop.java b/transport/src/main/java/io/netty/channel/nio/NioEventLoop.java
index d8eadf4a92..d04554a61a 100644
--- a/transport/src/main/java/io/netty/channel/nio/NioEventLoop.java
+++ b/transport/src/main/java/io/netty/channel/nio/NioEventLoop.java
@@ -137,7 +137,12 @@ public final class NioEventLoop extends SingleThreadEventLoop {
 
             Class<?> selectorImplClass =
                     Class.forName("sun.nio.ch.SelectorImpl", false, ClassLoader.getSystemClassLoader());
-            selectorImplClass.isAssignableFrom(selector.getClass());
+
+            // Ensure the current selector implementation is what we can instrument.
+            if (!selectorImplClass.isAssignableFrom(selector.getClass())) {
+                return selector;
+            }
+
             Field selectedKeysField = selectorImplClass.getDeclaredField("selectedKeys");
             Field publicSelectedKeysField = selectorImplClass.getDeclaredField("publicSelectedKeys");