diff --git a/build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/test/rest/transform/headers/InjectHeaders.java b/build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/test/rest/transform/headers/InjectHeaders.java
index a90903e1c1ca1..61470cd960237 100644
--- a/build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/test/rest/transform/headers/InjectHeaders.java
+++ b/build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/test/rest/transform/headers/InjectHeaders.java
@@ -31,8 +31,8 @@ public class InjectHeaders extends FeatureInjector implements RestTestTransformB
 
     private static JsonNodeFactory jsonNodeFactory = JsonNodeFactory.withExactBigDecimals(false);
 
-    private Map<String, String> headers;
-    private Set<Function<ObjectNode, Boolean>> applyConditions;
+    private final Map<String, String> headers;
+    private final Set<Function<ObjectNode, Boolean>> applyConditions;
 
     /**
      * @param headers The headers to inject