diff --git a/backend/controllers/userSheetProgressController.js b/backend/controllers/userSheetProgressController.js
index 3cdd267b..76c2bfc6 100644
--- a/backend/controllers/userSheetProgressController.js
+++ b/backend/controllers/userSheetProgressController.js
@@ -60,10 +60,15 @@ exports.saveProgress = async (req, res) => {
     });
   }
 
-  if (completedTopics !== undefined && !Array.isArray(completedTopics)) {
+  if (
+    completedTopics !== undefined &&
+    (typeof completedTopics !== "object" ||
+      completedTopics === null ||
+      Array.isArray(completedTopics))
+  ) {
     return res.status(400).json({
       success: false,
-      error: "Invalid completedTopics field, must be an array",
+      error: "Invalid completedTopics field, must be an object",
     });
   }