diff --git a/sphinx_immaterial/custom_admonitions.py b/sphinx_immaterial/custom_admonitions.py
index 86734b3a9..12054f7f1 100644
--- a/sphinx_immaterial/custom_admonitions.py
+++ b/sphinx_immaterial/custom_admonitions.py
@@ -43,7 +43,7 @@
 
 
 CSSClassType = Annotated[
-    str, pydantic.functional_validators.AfterValidator(nodes.make_id)
+    str, pydantic.AfterValidator(nodes.make_id)
 ]
 
 # defaults used for version directives re-styling