diff --git a/backend/blueprints/protect_pdf.py b/backend/blueprints/protect_pdf.py
index a6fbf7a..b32560a 100644
--- a/backend/blueprints/protect_pdf.py
+++ b/backend/blueprints/protect_pdf.py
@@ -70,7 +70,7 @@ def protect_pdf():
         return error("The uploaded file appears to be corrupted or is not a valid PDF.",400),
 
     except Exception as e:
-        return error("An error occurred while protecting the PDF: {str(e)}",500),
+        return error(f"An error occurred while protecting the PDF: {str(e)}",500),
 
     finally:
         if src: