diff --git a/src/calibre/ebooks/oeb/polish/check/parsing.py b/src/calibre/ebooks/oeb/polish/check/parsing.py
index 3cee4197f8..7e8878e0d3 100644
--- a/src/calibre/ebooks/oeb/polish/check/parsing.py
+++ b/src/calibre/ebooks/oeb/polish/check/parsing.py
@@ -330,6 +330,7 @@ class DuplicateId(BaseError):
 
 class InvalidId(BaseError):
 
+    level = WARN
     INDIVIDUAL_FIX = _(
         'Replace this id with a randomly generated valid id')