diff --git a/Script/CopyThread.py b/Script/CopyThread.py
index eebdca8e8ad10c3f5287b3c42762d2b144629b6d..6409e2e0ceaf794d8df524cabdceb7342902e0c6 100644
--- a/Script/CopyThread.py
+++ b/Script/CopyThread.py
@@ -313,7 +313,7 @@ class CopyThread(threading.Thread):
                 if remote_filesize:
                     # It is possible that the backend experienced an issue
                     if checksum is None:
-                        self.logger.critical('backend sizechecksum error for file %s: '
+                        self.logger.warning('backend sizechecksum error for file %s: '
                                 'filesize=%s, checksum=%s ; will retry later',
                                 CastorFile, str(remote_filesize), str(checksum))
                         # retry later