diff --git a/tests/test-qmp-input-strict.c b/tests/test-qmp-input-strict.c
index 0f77003..d5360c6 100644
--- a/tests/test-qmp-input-strict.c
+++ b/tests/test-qmp-input-strict.c
@@ -260,6 +260,21 @@
     qapi_free_UserDefFlatUnion(tmp);
 }
 
+static void test_validate_fail_union_flat_no_discrim(TestInputVisitorData *data,
+                                                     const void *unused)
+{
+    UserDefFlatUnion2 *tmp = NULL;
+    Error *err = NULL;
+    Visitor *v;
+
+    /* test situation where discriminator field ('enum1' here) is missing */
+    v = validate_test_init(data, "{ 'string': 'c', 'string1': 'd', 'string2': 'e' }");
+
+    visit_type_UserDefFlatUnion2(v, &tmp, NULL, &err);
+    g_assert(err);
+    qapi_free_UserDefFlatUnion2(tmp);
+}
+
 static void test_validate_fail_union_anon(TestInputVisitorData *data,
                                           const void *unused)
 {
@@ -310,6 +325,8 @@
                        &testdata, test_validate_fail_union);
     validate_test_add("/visitor/input-strict/fail/union-flat",
                        &testdata, test_validate_fail_union_flat);
+    validate_test_add("/visitor/input-strict/fail/union-flat-no-discriminator",
+                       &testdata, test_validate_fail_union_flat_no_discrim);
     validate_test_add("/visitor/input-strict/fail/union-anon",
                        &testdata, test_validate_fail_union_anon);