diff --git a/ets2panda/checker/ets/helpers.cpp b/ets2panda/checker/ets/helpers.cpp
index d6db10920758cd918746602136706ca2a7083632..c51f8fad4db578b4d1e7fd8bc12ef2d2424c9bce 100644
--- a/ets2panda/checker/ets/helpers.cpp
+++ b/ets2panda/checker/ets/helpers.cpp
@@ -2584,14 +2584,14 @@ bool ETSChecker::CheckLambdaAssignableUnion(ir::AstNode *typeAnn, ir::ScriptFunc
     bool assignable = false;
     for (auto *type : typeAnn->AsETSUnionType()->Types()) {
         if (type->IsETSFunctionType()) {
-            assignable |= lambda->Params().size() == type->AsETSFunctionType()->Params().size();
+            assignable |= lambda->Params().size() <= type->AsETSFunctionType()->Params().size();
             continue;
         }
 
         if (type->IsETSTypeReference()) {
             auto aliasType = util::Helpers::DerefETSTypeReference(type);
             assignable |= aliasType->IsETSFunctionType() &&
-                          lambda->Params().size() == aliasType->AsETSFunctionType()->Params().size();
+                          lambda->Params().size() <= aliasType->AsETSFunctionType()->Params().size();
         }
     }
 
diff --git a/ets2panda/test/runtime/ets/lambdaParamsInfer4.ets b/ets2panda/test/runtime/ets/lambdaParamsInfer4.ets
new file mode 100644
index 0000000000000000000000000000000000000000..1e12277b3592c0ff1279c348fa793d18e4abb177
--- /dev/null
+++ b/ets2panda/test/runtime/ets/lambdaParamsInfer4.ets
@@ -0,0 +1,19 @@
+/*
+ * 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.
+ */
+
+function foo(fun: ((a: number) => Int) | undefined) {
+    return 1;
+}
+arktest.assertEQ(foo((() => { return 1 })), 1);
diff --git a/ets2panda/test/runtime/ets/lambdaParamsInfer5.ets b/ets2panda/test/runtime/ets/lambdaParamsInfer5.ets
new file mode 100644
index 0000000000000000000000000000000000000000..b5dc3e873a8c2facf088d095cad7c95527048b06
--- /dev/null
+++ b/ets2panda/test/runtime/ets/lambdaParamsInfer5.ets
@@ -0,0 +1,20 @@
+/*
+ * 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.
+ */
+
+type callback = (a: number) => Int;
+function foo(fun: callback | undefined) {
+  return 1;
+}
+arktest.assertEQ(foo((() => { return 1 })), 1);