diff --git a/pgpainless-core/src/main/java/org/pgpainless/key/generation/KeyRingBuilder.java b/pgpainless-core/src/main/java/org/pgpainless/key/generation/KeyRingBuilder.java
index d0a6841f..063b1dc8 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/key/generation/KeyRingBuilder.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/key/generation/KeyRingBuilder.java
@@ -59,9 +59,9 @@ public class KeyRingBuilder implements KeyRingBuilderInterface {
 
     private final Charset UTF8 = Charset.forName("UTF-8");
 
-    private List<KeySpec> keySpecs = new ArrayList<>();
+    private final List<KeySpec> keySpecs = new ArrayList<>();
     private String userId;
-    private Set<String> additionalUserIds = new LinkedHashSet<>();
+    private final Set<String> additionalUserIds = new LinkedHashSet<>();
     private Passphrase passphrase;
 
     public PGPSecretKeyRing simpleRsaKeyRing(@Nonnull UserId userId, @Nonnull RsaLength length)
diff --git a/pgpainless-core/src/main/java/org/pgpainless/key/generation/KeySpecBuilder.java b/pgpainless-core/src/main/java/org/pgpainless/key/generation/KeySpecBuilder.java
index 4c7dd697..43e5e7d1 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/key/generation/KeySpecBuilder.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/key/generation/KeySpecBuilder.java
@@ -29,8 +29,8 @@ import org.pgpainless.key.generation.type.KeyType;
 
 public class KeySpecBuilder implements KeySpecBuilderInterface {
 
-    private KeyType type;
-    private PGPSignatureSubpacketGenerator hashedSubPackets = new PGPSignatureSubpacketGenerator();
+    private final KeyType type;
+    private final PGPSignatureSubpacketGenerator hashedSubPackets = new PGPSignatureSubpacketGenerator();
 
     KeySpecBuilder(@Nonnull KeyType type) {
         this.type = type;