diff --git a/api/src/app/services/book.service.ts b/api/src/app/services/book.service.ts
index d279f2c..638d302 100644
--- a/api/src/app/services/book.service.ts
+++ b/api/src/app/services/book.service.ts
@@ -48,7 +48,7 @@ export class BookService {
     if (data.coverImage) {
       if (data.coverImage.startsWith("data:")) {
         const sizeInBytes = data.coverImage.length * 0.75;
-        if (sizeInBytes > MAX_LENGTHS.IMAGE_DATA) {
+        if (sizeInBytes > MAX_LENGTHS.DATA_URL) {
           throw new Error("Cover image must be under 5MB.");
         }
         if (!validateDataUrl(data.coverImage)) {