diff --git a/src/main/java/net/schmizz/sshj/common/Buffer.java b/src/main/java/net/schmizz/sshj/common/Buffer.java
index 4386d29a..bf5f1fc5 100644
--- a/src/main/java/net/schmizz/sshj/common/Buffer.java
+++ b/src/main/java/net/schmizz/sshj/common/Buffer.java
@@ -51,7 +51,7 @@ public class Buffer<T extends Buffer<T>> {
         }
     }
 
-    public static class PlainBuffer
+    public static final class PlainBuffer
             extends Buffer<PlainBuffer> {
 
         public PlainBuffer() {
diff --git a/src/main/java/net/schmizz/sshj/common/SSHPacket.java b/src/main/java/net/schmizz/sshj/common/SSHPacket.java
index f0374e42..abf93c6f 100644
--- a/src/main/java/net/schmizz/sshj/common/SSHPacket.java
+++ b/src/main/java/net/schmizz/sshj/common/SSHPacket.java
@@ -37,7 +37,7 @@ package net.schmizz.sshj.common;
 
 import java.util.Arrays;
 
-public class SSHPacket
+public final class SSHPacket
         extends Buffer<SSHPacket> {
 
     public SSHPacket() {
diff --git a/src/main/java/net/schmizz/sshj/sftp/Request.java b/src/main/java/net/schmizz/sshj/sftp/Request.java
index 4a6466eb..39a99bf0 100644
--- a/src/main/java/net/schmizz/sshj/sftp/Request.java
+++ b/src/main/java/net/schmizz/sshj/sftp/Request.java
@@ -17,7 +17,7 @@ package net.schmizz.sshj.sftp;
 
 import net.schmizz.concurrent.Promise;
 
-public class Request
+public final class Request
         extends SFTPPacket<Request> {
 
     private final PacketType type;
diff --git a/src/main/java/net/schmizz/sshj/sftp/Response.java b/src/main/java/net/schmizz/sshj/sftp/Response.java
index 92ad141a..59bbcff0 100644
--- a/src/main/java/net/schmizz/sshj/sftp/Response.java
+++ b/src/main/java/net/schmizz/sshj/sftp/Response.java
@@ -17,7 +17,7 @@ package net.schmizz.sshj.sftp;
 
 import net.schmizz.sshj.common.Buffer;
 
-public class Response
+public final class Response
         extends SFTPPacket<Response> {
 
     public static enum StatusCode {