diff --git a/.changeset/hungry-eyes-film.md b/.changeset/hungry-eyes-film.md
new file mode 100644
index 0000000..9aacf89
--- /dev/null
+++ b/.changeset/hungry-eyes-film.md
@@ -0,0 +1,5 @@
+---
+"@jacksonneal/ts-standard": patch
+---
+
+testing
diff --git a/libs/ts-standard/ex/type.ex.ts b/libs/ts-standard/ex/type.ex.ts
index 48b878a..43c4ba3 100644
--- a/libs/ts-standard/ex/type.ex.ts
+++ b/libs/ts-standard/ex/type.ex.ts
@@ -11,6 +11,8 @@ import { is } from "./shared.ex";
 // Opt<T>
 is<Opt<string>>("hello");
 is<Opt<string>>(null);
+// @ts-expect-error `undefined` is not `Opt`
+is<Opt<string>>(undefined);
 
 // Nullable<T>
 is<Nullable<string>>("hello");