diff --git a/ets2panda/test/runtime/ets/BigInt5.ets b/ets2panda/test/runtime/ets/BigInt5.ets
index 9f5ea07be22ef568dc748234220190456327a78f..50c939f603a560446b70ef32d74e910c3e1d91a6 100644
--- a/ets2panda/test/runtime/ets/BigInt5.ets
+++ b/ets2panda/test/runtime/ets/BigInt5.ets
@@ -89,7 +89,13 @@ function test_unary(): void {
     arktest.assertEQ(b.toString(), "-321")
 }
 
+function test_undefined(): void {
+    let n = 10n
+    arktest.assertEQ(n.toString(undefined), "10")
+}
+
 function main() : void {
     test_unary()
     test_unary_minus()
+    test_undefined()
 }