diff --git a/sphinx_immaterial/apidoc/generic_synopses.py b/sphinx_immaterial/apidoc/generic_synopses.py
index 492117b3f..3f0a5466f 100644
--- a/sphinx_immaterial/apidoc/generic_synopses.py
+++ b/sphinx_immaterial/apidoc/generic_synopses.py
@@ -140,7 +140,7 @@ def resolve_any_xref(
                 docname, labelid = self.objects[key]
                 results.append(
                     (
-                        "std:" + self.role_for_objtype(objtype),
+                        "std:" + cast(str, self.role_for_objtype(objtype)),
                         make_refnode(
                             self,
                             builder,