diff --git a/engine/baml-lib/baml/tests/validation_files/functions_v2/check_in_parameter.baml b/engine/baml-lib/baml/tests/validation_files/functions_v2/check_in_parameter.baml
new file mode 100644
index 000000000..bece0ae27
--- /dev/null
+++ b/engine/baml-lib/baml/tests/validation_files/functions_v2/check_in_parameter.baml
@@ -0,0 +1,24 @@
+client<llm> MyClient {
+  provider baml-openai-chat
+}
+
+class Foo {
+  bar Bar?
+  baz int
+}
+
+class Bar {
+  name string @check({{ this|length > 0 }}, nonempty_name)
+}
+
+function Go(a: Foo) -> int {
+  client MyClient
+  prompt #"Hi"#
+}
+
+// error: Error validating: Types with checks are not allowed as function parameters.
+//   -->  functions_v2/check_in_parameter.baml:14
+//    | 
+// 13 | 
+// 14 | function Go(a: Foo) -> int {
+//    | 
diff --git a/engine/language_client_typescript/checked.d.ts b/engine/language_client_typescript/checked.d.ts
new file mode 100644
index 000000000..b4a4ce27c
--- /dev/null
+++ b/engine/language_client_typescript/checked.d.ts
@@ -0,0 +1,14 @@
+export interface Checked<T, K extends BaseChecks> {
+    value: T;
+    checks: K;
+}
+interface Check {
+    name: string;
+    expr: string;
+    result: "succeeded" | "failed";
+}
+interface BaseChecks {
+    [key: string]: Check;
+}
+export {};
+//# sourceMappingURL=checked.d.ts.map
\ No newline at end of file
diff --git a/engine/language_client_typescript/checked.d.ts.map b/engine/language_client_typescript/checked.d.ts.map
new file mode 100644
index 000000000..65e7e30a7
--- /dev/null
+++ b/engine/language_client_typescript/checked.d.ts.map
@@ -0,0 +1 @@
+{"version":3,"file":"checked.d.ts","sourceRoot":"","sources":["typescript_src/checked.ts"],"names":[],"mappings":"AAAA,MAAM,WAAW,OAAO,CAAC,CAAC,EAAC,CAAC,SAAS,UAAU;IAC3C,KAAK,EAAE,CAAC,CAAC;IACT,MAAM,EAAE,CAAC,CAAC;CACb;AAED,UAAU,KAAK;IACX,IAAI,EAAE,MAAM,CAAC;IACb,IAAI,EAAE,MAAM,CAAA;IACZ,MAAM,EAAE,WAAW,GAAG,QAAQ,CAAA;CACjC;AAED,UAAU,UAAU;IAChB,CAAC,GAAG,EAAE,MAAM,GAAG,KAAK,CAAA;CACvB"}
\ No newline at end of file
diff --git a/engine/language_client_typescript/checked.js b/engine/language_client_typescript/checked.js
new file mode 100644
index 000000000..00a461ab4
--- /dev/null
+++ b/engine/language_client_typescript/checked.js
@@ -0,0 +1,5 @@
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+function all_succeeded(checks) {
+    return Object.values(checks).every(value => value.result == "succeeded");
+}