diff --git a/ets2panda/ir/expressions/memberExpression.cpp b/ets2panda/ir/expressions/memberExpression.cpp
index 016e43c9e5d561f6d18a8326d0167ae20709b249..b7df6f2ab23ce3b1f18ef8a80e38408b3a6c9618 100644
--- a/ets2panda/ir/expressions/memberExpression.cpp
+++ b/ets2panda/ir/expressions/memberExpression.cpp
@@ -227,6 +227,11 @@ checker::Type *MemberExpression::TraverseUnionMember(checker::ETSChecker *checke
             return;
         }
 
+        if(!commonPropType->IsETSFunctionType() || !memberType->IsETSFunctionType()) {
+            checker->LogError(diagnostic::MEMBER_TYPE_MISMATCH_ACROSS_UNION, {}, Start());
+            return;
+        }
+
         auto newType =
             checker->IntersectSignatureSets(commonPropType->AsETSFunctionType(), memberType->AsETSFunctionType());
         if (newType->AsETSFunctionType()->CallSignatures().empty()) {
diff --git a/ets2panda/test/ast/compiler/ets/union_objects_with_different_member_types.ets b/ets2panda/test/ast/compiler/ets/union_objects_with_different_member_types.ets
new file mode 100644
index 0000000000000000000000000000000000000000..a421772e1abec60db89f2ebe1195cf325b608224
--- /dev/null
+++ b/ets2panda/test/ast/compiler/ets/union_objects_with_different_member_types.ets
@@ -0,0 +1,39 @@
+/*
+ * Copyright (c) 2025 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.
+ */
+
+interface I {
+    foo?:() => void;
+}
+
+class A {
+    foo(): void {
+        console.log('original');
+    }
+}
+
+let u: I | A = new A();
+
+function main() {
+    u.foo = () => {
+        console.log('test');
+    };
+
+    u.foo();
+}
+
+/* @@? 29:5 Error TypeError: Member type must be the same for all union objects. */
+/* @@? 33:5 Error TypeError: Member type must be the same for all union objects. */
+/* @@? 33:5 Error TypeError: Value is possibly nullish. */
+/* @@? 33:5 Error TypeError: Type '() => void|undefined' has no call signatures. */