diff --git a/test_lisp.c b/test_lisp.c
index 908a8b7..470ab6e 100644
--- a/test_lisp.c
+++ b/test_lisp.c
@@ -219,4 +219,7 @@ Test(lisp, set) {
     v = eval_string("(define x 1) (set! x 42) x");
     cr_assert(value_is_int(v));
     cr_assert_eq(42, value_to_int(v));
+
+    v = eval_string("(set! x 42) x");
+    assert_runtime_error(v, "unbound variable x");
 }