diff --git a/ets2panda/checker/ets/function.cpp b/ets2panda/checker/ets/function.cpp
index 317fc2afcbd80ce89cacd11494ebb3b23deb6e3b..98b2fd7e4760d2fc8d3e080febb0450c395f35cf 100644
--- a/ets2panda/checker/ets/function.cpp
+++ b/ets2panda/checker/ets/function.cpp
@@ -1435,7 +1435,11 @@ static bool CollectOverload(checker::ETSChecker *checker, ir::MethodDefinition *
     ArenaVector<ETSFunctionType *> overloads(checker->ProgramAllocator()->Adapter());
 
     for (ir::MethodDefinition *const currentFunc : method->Overloads()) {
-        ldInfo.isDeclare &= currentFunc->IsDeclare();
+        if (currentFunc->IsDeclare() != ldInfo.isDeclare) {
+            checker->LogError(diagnostic::AMBIGUOUS_AMBIENT, {currentFunc->Id()->Name()}, currentFunc->Start());
+            method->Id()->Variable()->SetTsType(checker->GlobalTypeError());
+            return false;
+        }
         ES2PANDA_ASSERT(currentFunc->Function() != nullptr);
         ES2PANDA_ASSERT(currentFunc->Id() != nullptr);
         currentFunc->Function()->Id()->SetVariable(currentFunc->Id()->Variable());
diff --git a/ets2panda/test/ast/compiler/ets/ambient_function.ets b/ets2panda/test/ast/compiler/ets/ambient_function.ets
new file mode 100644
index 0000000000000000000000000000000000000000..7f20bea7e3be6d1b0e1abfbbdf848db4ecef2343
--- /dev/null
+++ b/ets2panda/test/ast/compiler/ets/ambient_function.ets
@@ -0,0 +1,28 @@
+/*
+ * 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.
+ */
+
+let a1: [number] | null = null;
+let a2: [number] = [0x00000001];
+
+declare function capset(...p: [number]): void;
+
+function capset(...p: [number]) {}
+
+function main() {
+  capset(...(a1 ?? a2));
+}
+
+/* @@? 21:1 Error TypeError: Method declaration `capset` must all ambient or non-ambient */
+/* @@? 24:3 Error TypeError: This expression is not callable. */
diff --git a/ets2panda/test/ast/compiler/ets/same_assembly_overload/overload_signature_neg_2.ets b/ets2panda/test/ast/compiler/ets/same_assembly_overload/overload_signature_neg_2.ets
index 27671485ba3f5d7637c94c0fb5767e439e97f762..18bdf1ec9ef90f3ca5698970adb7c7e35c47de6d 100644
--- a/ets2panda/test/ast/compiler/ets/same_assembly_overload/overload_signature_neg_2.ets
+++ b/ets2panda/test/ast/compiler/ets/same_assembly_overload/overload_signature_neg_2.ets
@@ -18,4 +18,4 @@ export class A<T> {}
 export declare function foo(a:A<number>):void
 export function foo(a:A<string>):number {}
 
-/* @@? 19:17 Error TypeError: Function with a non void return type must return a value. */
+/* @@? 19:8 Error TypeError: Method declaration `foo` must all ambient or non-ambient */
diff --git a/ets2panda/util/diagnostic/semantic.yaml b/ets2panda/util/diagnostic/semantic.yaml
index 2db429ba584df212f5b29839397c1a6fc7328b61..986428b56f954313c1789a1148a1e6d9307cbed2 100644
--- a/ets2panda/util/diagnostic/semantic.yaml
+++ b/ets2panda/util/diagnostic/semantic.yaml
@@ -69,6 +69,10 @@ semantic:
   id: 175
   message: "A 'const' initializer in an ambient context must be a string or numeric literal: {}"
 
+- name: AMBIGUOUS_AMBIENT
+  id: 399
+  message: "Method declaration `{}` must all ambient or non-ambient"
+
 - name: AMBIGUOUS_CALL
   id: 142
   message: "Call to `{}` is ambiguous as `2` versions of `{}` are available: `{}{}` and `{}{}`"