diff --git a/pgpainless-core/src/main/java/org/pgpainless/decryption_verification/ConsumerOptions.java b/pgpainless-core/src/main/java/org/pgpainless/decryption_verification/ConsumerOptions.java
index dba9fca7..0f02aba0 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/decryption_verification/ConsumerOptions.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/decryption_verification/ConsumerOptions.java
@@ -49,7 +49,7 @@ public class ConsumerOptions {
 
     // Session key for decryption without passphrase/key
     private SessionKey sessionKey = null;
-    private Map<Long, PublicKeyDataDecryptorFactory> customPublicKeyDataDecryptorFactories = new HashMap<>();
+    private final Map<Long, PublicKeyDataDecryptorFactory> customPublicKeyDataDecryptorFactories = new HashMap<>();
 
     private final Map<PGPSecretKeyRing, SecretKeyRingProtector> decryptionKeys = new HashMap<>();
     private final Set<Passphrase> decryptionPassphrases = new HashSet<>();