diff --git a/qutil/domains.py b/qutil/domains.py
index 1bce56748bdaecb5f4b6a2aa7455903c0e86c9dc..524df27aa6f2016b0b40171f3cabd89f376e1e4d 100644
--- a/qutil/domains.py
+++ b/qutil/domains.py
@@ -422,7 +422,7 @@ class BoundedSet(frozenset, Domain[_RealT], Bounded[_RealT]):
                 and self.round(value) in self._rounded)
 
     @cached_property
-    def _rounded(self) -> set[_RealT]:
+    def _rounded(self) -> Set[_RealT]:
         return {self.round(item) for item in self}
 
     def min(self) -> _RealT: