diff --git a/lang/interpret_test/TestAstFunc2/ycombinator.txtar b/lang/interpret_test/TestAstFunc2/ycombinator.txtar
new file mode 100644
index 00000000..43c7cd7c
--- /dev/null
+++ b/lang/interpret_test/TestAstFunc2/ycombinator.txtar
@@ -0,0 +1,14 @@
+-- main.mcl --
+import "fmt"
+
+$y = func($fn) {
+	$fn($fn)
+}(
+	func($fn) {
+		$fn($fn)
+	}
+)
+
+test [fmt.printf("y: %v", $y),] {}
+-- OUTPUT --
+# err: errUnify: unify error with: param(fn): directly in the same set