diff --git a/httpclient/src/main/java/org/apache/http/impl/auth/NTLMEngineImpl.java b/httpclient/src/main/java/org/apache/http/impl/auth/NTLMEngineImpl.java
index 216f43f45..70cbe50d4 100644
--- a/httpclient/src/main/java/org/apache/http/impl/auth/NTLMEngineImpl.java
+++ b/httpclient/src/main/java/org/apache/http/impl/auth/NTLMEngineImpl.java
@@ -770,7 +770,7 @@ final class NTLMEngineImpl implements NTLMEngine {
         final private byte[] exportedSessionKey;
         private byte[] signingKey;
         private byte[] sealingKey;
-        private Cipher rc4;
+        private final Cipher rc4;
         final Mode mode;
         final private boolean isConnection;
         int sequenceNumber = 0;