diff --git a/java/org/slub/rosetta/dps/repository/plugin/Validation/SLUBValidateRelaxNG.java b/java/org/slub/rosetta/dps/repository/plugin/Validation/SLUBValidateRelaxNG.java
index bffbe05e0dc5a57da98eebc870c78f888518ca92..23ee118495741fae5a0968d63d9fb9a360acda09 100644
--- a/java/org/slub/rosetta/dps/repository/plugin/Validation/SLUBValidateRelaxNG.java
+++ b/java/org/slub/rosetta/dps/repository/plugin/Validation/SLUBValidateRelaxNG.java
@@ -19,7 +19,7 @@ import java.util.List;
 
 public class SLUBValidateRelaxNG {
     private boolean is_valid = true;
-    private List<String> errors = new ArrayList<>();
+    private final List<String> errors = new ArrayList<>();
     public SLUBValidateRelaxNG() {
     }
 
diff --git a/java/org/slub/rosetta/dps/repository/plugin/Validation/SLUBValidateSchema.java b/java/org/slub/rosetta/dps/repository/plugin/Validation/SLUBValidateSchema.java
index 10f7386a6cd9d3242fad808532dd4fbe4d998525..1adb7bb2e831f47c31fd4078f22270f53abfbda1 100644
--- a/java/org/slub/rosetta/dps/repository/plugin/Validation/SLUBValidateSchema.java
+++ b/java/org/slub/rosetta/dps/repository/plugin/Validation/SLUBValidateSchema.java
@@ -15,7 +15,7 @@ import java.net.URI;
 
 public class SLUBValidateSchema {
 
-    private ValidationResourceResolver validationResourceResolver;
+    private final ValidationResourceResolver validationResourceResolver;
     public SLUBValidateSchema(ValidationResourceResolver validationResourceResolver) {
         this.validationResourceResolver = validationResourceResolver;
     }