diff --git a/lib_afc_s3storage/s3storage.py b/lib_afc_s3storage/s3storage.py
index 892f354..5ae202f 100755
--- a/lib_afc_s3storage/s3storage.py
+++ b/lib_afc_s3storage/s3storage.py
@@ -101,8 +101,8 @@ class S3Storage:
 
         if filepathname is None:
             raise AFS3Error("S3Storage.upload_file(): missing required filepathname")
-        elif not os.path.exists(filepathname):
-            raise AFS3Error("S3Storage.upload_file(): invalid filepathname '%s'", filepathname)
+        if not os.path.exists(filepathname):
+            raise AFS3Error(f"S3Storage.upload_file(): invalid filepathname '{filepathname}'")
 
         if bucket is None:
             raise AFS3Error("S3Storage.upload_file(): missing required bucket name")