diff --git a/arkindex_worker/worker/element.py b/arkindex_worker/worker/element.py
index 32b9694978924e2d479b67b376cb406900ed7c50..f751b19b632416e4b86c695df86db5c2a555e126 100644
--- a/arkindex_worker/worker/element.py
+++ b/arkindex_worker/worker/element.py
@@ -31,7 +31,7 @@ class ElementMixin(object):
 
         if missing_slugs:
             raise MissingTypeError(
-                f'Element type(s) {", ".join(missing_slugs)} were not found in the {corpus["name"]} corpus ({corpus["id"]}).'
+                f'Element type(s) {", ".join(sorted(missing_slugs))} were not found in the {corpus["name"]} corpus ({corpus["id"]}).'
             )
 
         return True