diff --git a/transport-native-epoll/src/main/java/io/netty/channel/epoll/EpollEventLoop.java b/transport-native-epoll/src/main/java/io/netty/channel/epoll/EpollEventLoop.java
index 909088fde4..2607615117 100644
--- a/transport-native-epoll/src/main/java/io/netty/channel/epoll/EpollEventLoop.java
+++ b/transport-native-epoll/src/main/java/io/netty/channel/epoll/EpollEventLoop.java
@@ -350,6 +350,8 @@ final class EpollEventLoop extends SingleThreadEventLoop {
         } catch (IOException ignore) {
             // ignore on close
         }
+        // Using the intermediate collection to prevent ConcurrentModificationException.
+        // In the `close()` method, the channel is deleted from `channels` map.
         Collection<AbstractEpollChannel> array = new ArrayList<AbstractEpollChannel>(channels.size());
 
         for (AbstractEpollChannel channel: channels.values()) {