diff --git a/ets2panda/checker/types/ets/etsTypeParameter.cpp b/ets2panda/checker/types/ets/etsTypeParameter.cpp
index d19a6ef1162b28ee9fc728d3aad613230c6d612d..f747631ae6d5943844182b2e330607eb2db5f9b6 100644
--- a/ets2panda/checker/types/ets/etsTypeParameter.cpp
+++ b/ets2panda/checker/types/ets/etsTypeParameter.cpp
@@ -144,8 +144,7 @@ Type *ETSTypeParameter::Substitute(TypeRelation *relation, const Substitution *s
         if (this != original && ((ContainsNull() && !repl_type->ContainsNull()) ||
                                  (ContainsUndefined() && !repl_type->ContainsUndefined()))) {
             // this type is explicitly marked as nullish
-            ASSERT(repl_type->IsETSObjectType() || repl_type->IsETSArrayType() || repl_type->IsETSFunctionType() ||
-                   repl_type->IsETSTypeParameter());
+            ASSERT(ETSChecker::IsReferenceType(repl_type));
             auto nullish_flags = TypeFlag(TypeFlags() & TypeFlag::NULLISH);
             auto *new_repl_type = checker->CreateNullishType(repl_type, nullish_flags, checker->Allocator(), relation,
                                                              checker->GetGlobalTypesHolder());
diff --git a/ets2panda/test/runtime/ets/generic_constructor_with_union.ets b/ets2panda/test/runtime/ets/generic_constructor_with_union.ets
new file mode 100644
index 0000000000000000000000000000000000000000..4ec5964d829f315163a3b5cb5c75ebd0cdfeab1c
--- /dev/null
+++ b/ets2panda/test/runtime/ets/generic_constructor_with_union.ets
@@ -0,0 +1,18 @@
+/*
+ * Copyright (c) 2023 Huawei Device Co., Ltd.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+function main(): void {
+   let x = new Array<(Number|String)>();
+}
\ No newline at end of file