diff --git a/ets2panda/parser/statementParser.cpp b/ets2panda/parser/statementParser.cpp
index 86f766bedcc0252c8688b7a7fe7be0a5365f29d7..81e2951a86a6a82626ca328725dbf7ae47eeed54 100644
--- a/ets2panda/parser/statementParser.cpp
+++ b/ets2panda/parser/statementParser.cpp
@@ -167,6 +167,10 @@ ir::Statement *ParserImpl::ParseStatementBasedOnTokenType(StatementParsingFlags
     switch (lexer_->GetToken().Type()) {
         case lexer::TokenType::KEYW_EXPORT:
             return ParseExportDeclaration(flags);
+        case lexer::TokenType::KEYW_EXTENDS:
+            LogError(diagnostic::ERROR_ARKTS_NO_CONDITIONAL_TYPES);
+            lexer_->NextToken();
+            return nullptr;
         case lexer::TokenType::KEYW_IMPORT:
             return ParseImportDeclaration(flags);
         case lexer::TokenType::KEYW_FUNCTION:
diff --git a/ets2panda/test/ast/compiler/ets/conditional-type-alias.ets b/ets2panda/test/ast/compiler/ets/conditional-type-alias.ets
new file mode 100644
index 0000000000000000000000000000000000000000..095f6a96801035f8cdcf40f85bda0babea4b5789
--- /dev/null
+++ b/ets2panda/test/ast/compiler/ets/conditional-type-alias.ets
@@ -0,0 +1,22 @@
+/*
+ * 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.
+ */
+
+// (arkts-no-conditional-types)
+type X<T> = T extends number ? T : string
+
+/* @@? 17:15 Error TypeError: Conditional type aliases are not supported. Introduce a new type with constraints explicitly, or rewrite logic using Object! */
+/* @@? 17:23 Error TypeError: Type name 'number' used in the wrong context */
+/* @@? 17:32 Error TypeError: TypeError: Unresolved reference T */
+/* @@? 17:36 Error TypeError: Type name 'string' used in the wrong context */
diff --git a/ets2panda/util/diagnostic/semantic.yaml b/ets2panda/util/diagnostic/semantic.yaml
index 568a3b73128a4625368f0bb392f21c0762ebe352..8285f973c362f9c063efe7cd827448ab2f7aba9c 100644
--- a/ets2panda/util/diagnostic/semantic.yaml
+++ b/ets2panda/util/diagnostic/semantic.yaml
@@ -1496,5 +1496,9 @@ semantic:
   message: "Class field '{}' defined by the parent class is not accessible in the child class via super."
 
 - name: INTERFACE_EXTENDS_CLASS
-  id: 373
+  id: 378
   message: "Interfaces cannot extend classes, only other interfaces."
+
+- name: ERROR_ARKTS_NO_CONDITIONAL_TYPES
+  id: 379
+  message: "Conditional type aliases are not supported. Introduce a new type with constraints explicitly, or rewrite logic using Object!"
\ No newline at end of file