diff --git a/src/main/java/stirling/software/SPDF/controller/api/misc/ReplaceAndInvertColorController.java b/src/main/java/stirling/software/SPDF/controller/api/misc/ReplaceAndInvertColorController.java
index 927b3a51f..865724a74 100644
--- a/src/main/java/stirling/software/SPDF/controller/api/misc/ReplaceAndInvertColorController.java
+++ b/src/main/java/stirling/software/SPDF/controller/api/misc/ReplaceAndInvertColorController.java
@@ -25,7 +25,7 @@ import stirling.software.SPDF.service.misc.ReplaceAndInvertColorService;
 @RequiredArgsConstructor
 public class ReplaceAndInvertColorController {
 
-    private ReplaceAndInvertColorService replaceAndInvertColorService;
+    private final ReplaceAndInvertColorService replaceAndInvertColorService;
 
     @PostMapping(consumes = "multipart/form-data", value = "/replace-invert-pdf")
     @Operation(
diff --git a/src/main/java/stirling/software/SPDF/service/misc/ReplaceAndInvertColorService.java b/src/main/java/stirling/software/SPDF/service/misc/ReplaceAndInvertColorService.java
index 20c20eb7b..e2a4e7ea5 100644
--- a/src/main/java/stirling/software/SPDF/service/misc/ReplaceAndInvertColorService.java
+++ b/src/main/java/stirling/software/SPDF/service/misc/ReplaceAndInvertColorService.java
@@ -16,7 +16,7 @@ import stirling.software.SPDF.utils.misc.ReplaceAndInvertColorStrategy;
 @Service
 @RequiredArgsConstructor
 public class ReplaceAndInvertColorService {
-    private ReplaceAndInvertColorFactory replaceAndInvertColorFactory;
+    private final ReplaceAndInvertColorFactory replaceAndInvertColorFactory;
 
     public InputStreamResource replaceAndInvertColor(
             MultipartFile file,