diff --git a/ets2panda/parser/ETSparser.h b/ets2panda/parser/ETSparser.h
index 738bc9f53f929088ad83aeee77a2e4335543c760..01cca2560c3e5b933800b7c2fb03d74ccd3fc0fb 100644
--- a/ets2panda/parser/ETSparser.h
+++ b/ets2panda/parser/ETSparser.h
@@ -440,6 +440,7 @@ private:
     // NOLINTNEXTLINE(google-default-arguments)
     ir::Expression *ParseExpression(ExpressionParseFlags flags = ExpressionParseFlags::NO_OPTS) override;
     ir::Expression *ParseExpressionOrTypeAnnotation(lexer::TokenType type, ExpressionParseFlags flags) override;
+    void ValidateKeywordIn();
     ir::Expression *ParsePotentialExpressionSequence(ir::Expression *expr, ExpressionParseFlags flags) override;
     ir::Expression *ParseGenericLambdaOrTypeAssertion();
     ir::ModifierFlags ParseTypeVarianceModifier(TypeAnnotationParsingOptions *const options);
diff --git a/ets2panda/parser/ETSparserExpressions.cpp b/ets2panda/parser/ETSparserExpressions.cpp
index 8d990614716770414f54c64351825353890d6cd5..938d3be96065bd069018e891191296cfab13d786 100644
--- a/ets2panda/parser/ETSparserExpressions.cpp
+++ b/ets2panda/parser/ETSparserExpressions.cpp
@@ -839,6 +839,21 @@ ir::Expression *ETSParser::ParseGenericLambdaOrTypeAssertion()
     return AllocBrokenExpression(lexer::SourceRange {start, Lexer()->GetToken().End()});
 }
 
+void ETSParser::ValidateKeywordIn()
+{
+    if (Lexer()->GetToken().KeywordType() == lexer::TokenType::KEYW_IN) {
+        LogError(diagnostic::ERROR_ARKTS_NO_IN_OPERATOR);
+        Lexer()->NextToken();  // eat 'in'
+        if (auto const tokenType = Lexer()->GetToken().Type(); tokenType == lexer::TokenType::PUNCTUATOR_LEFT_BRACE) {
+            ParseObjectExpression();
+        } else if (tokenType == lexer::TokenType::PUNCTUATOR_LEFT_SQUARE_BRACKET) {
+            ParseArrayExpression(ExpressionParseFlags::NO_OPTS);
+        } else {
+            Lexer()->NextToken();
+        }
+    }
+}
+
 // NOLINTNEXTLINE(google-default-arguments)
 ir::Expression *ETSParser::ParseExpression(ExpressionParseFlags flags)
 {
@@ -866,6 +881,7 @@ ir::Expression *ETSParser::ParseExpression(ExpressionParseFlags flags)
     }
 
     ir::Expression *unaryExpressionNode = ParseUnaryOrPrefixUpdateExpression(flags);
+    ValidateKeywordIn();
     if ((flags & ExpressionParseFlags::INSTANCEOF) != 0) {
         ValidateInstanceOfExpression(unaryExpressionNode);
     }
@@ -873,12 +889,9 @@ ir::Expression *ETSParser::ParseExpression(ExpressionParseFlags flags)
     ir::Expression *assignmentExpression = ParseAssignmentExpression(unaryExpressionNode, flags);
     ApplyAnnotationsToNode(assignmentExpression, std::move(annotations), start);
 
-    if (Lexer()->GetToken().NewLine()) {
-        return assignmentExpression;
-    }
-
-    if (Lexer()->GetToken().Type() == lexer::TokenType::PUNCTUATOR_COMMA &&
-        (flags & ExpressionParseFlags::ACCEPT_COMMA) != 0U && (flags & ExpressionParseFlags::IN_FOR) != 0U) {
+    if (!Lexer()->GetToken().NewLine() &&
+        (Lexer()->GetToken().Type() == lexer::TokenType::PUNCTUATOR_COMMA &&
+         (flags & ExpressionParseFlags::ACCEPT_COMMA) != 0U && (flags & ExpressionParseFlags::IN_FOR) != 0U)) {
         return ParseSequenceExpression(assignmentExpression, (flags & ExpressionParseFlags::ACCEPT_REST) != 0U);
     }
 
diff --git a/ets2panda/test/ast/compiler/ets/noInOperator.ets b/ets2panda/test/ast/compiler/ets/noInOperator.ets
new file mode 100644
index 0000000000000000000000000000000000000000..27aa68a1ccfc0200e99df36f86cc1f831246ce6c
--- /dev/null
+++ b/ets2panda/test/ast/compiler/ets/noInOperator.ets
@@ -0,0 +1,26 @@
+/*
+ * 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.
+ */
+
+class Person {
+  name: string = ""
+}
+let p = new Person()
+let b = "name" /* @@ label1 */in p
+let c = "name" /* @@ label2 */in {name: 1, some: 2}
+let d = 2 /* @@ label3 */in [44, 55]
+
+/* @@@ label1 Error SyntaxError: 'in' operator is not supported. Use 'instanceof' operator to check whether an object is the instance of a class that contains the necessary class member. */
+/* @@@ label2 Error SyntaxError: 'in' operator is not supported. Use 'instanceof' operator to check whether an object is the instance of a class that contains the necessary class member. */
+/* @@@ label3 Error SyntaxError: 'in' operator is not supported. Use 'instanceof' operator to check whether an object is the instance of a class that contains the necessary class member. */
diff --git a/ets2panda/test/ast/parser/ets/FixedArray/InvalidStatements3.ets b/ets2panda/test/ast/parser/ets/FixedArray/InvalidStatements3.ets
index ef5fb160524f486bcf001ae132a3c0868e648940..a285e8f19e9c99873b23b759129755562c577065 100644
--- a/ets2panda/test/ast/parser/ets/FixedArray/InvalidStatements3.ets
+++ b/ets2panda/test/ast/parser/ets/FixedArray/InvalidStatements3.ets
@@ -59,5 +59,6 @@ for (let i = 1 in [0, 1, 2]) {}
 /* @@? 38:5 Error SyntaxError: Unexpected token 'private'. */
 /* @@? 38:13 Error SyntaxError: Unexpected token '@'. */
 /* @@? 38:14 Error TypeError: Cannot find type 'annotate'. */
-/* @@? 42:16 Error SyntaxError: for-in loop variable declaration may not have an initializer. */
-/* @@? 42:16 Error SyntaxError: 'for ... in' loop is not supported, please use regular 'for' or 'for ... of ...' loop to iterate through arrays and iterable objects. */
+/* @@? 42:16 Error SyntaxError: 'in' operator is not supported. Use 'instanceof' operator to check whether an object is the instance of a class that contains the necessary class member. */
+/* @@? 42:28 Error SyntaxError: Expected ';', got ')'. */
+/* @@? 42:28 Error SyntaxError: Invalid left-hand side in 'For[In/Of]Statement'. */
diff --git a/ets2panda/test/ast/parser/ets/InvalidStatements3.ets b/ets2panda/test/ast/parser/ets/InvalidStatements3.ets
index 308ab7542c9dc3dca8077fb5dfc665065e625eba..b22649104ee05fa1d0b541ad3ae1108aaef69abd 100644
--- a/ets2panda/test/ast/parser/ets/InvalidStatements3.ets
+++ b/ets2panda/test/ast/parser/ets/InvalidStatements3.ets
@@ -59,5 +59,6 @@ for (let i = 1 in [0, 1, 2]) {}
 /* @@? 38:5 Error SyntaxError: Unexpected token 'private'. */
 /* @@? 38:13 Error SyntaxError: Unexpected token '@'. */
 /* @@? 38:14 Error TypeError: Cannot find type 'annotate'. */
-/* @@? 42:16 Error SyntaxError: for-in loop variable declaration may not have an initializer. */
-/* @@? 42:16 Error SyntaxError: 'for ... in' loop is not supported, please use regular 'for' or 'for ... of ...' loop to iterate through arrays and iterable objects. */
+/* @@? 42:16 Error SyntaxError: 'in' operator is not supported. Use 'instanceof' operator to check whether an object is the instance of a class that contains the necessary class member. */
+/* @@? 42:28 Error SyntaxError: Expected ';', got ')'. */
+/* @@? 42:28 Error SyntaxError: Invalid left-hand side in 'For[In/Of]Statement'. */
diff --git a/ets2panda/util/diagnostic/syntax.yaml b/ets2panda/util/diagnostic/syntax.yaml
index 6665016a2ed312d820e61ea8c4e508069c15ce8b..3f964a674677cedc1d1b730152e919f91407ae41 100644
--- a/ets2panda/util/diagnostic/syntax.yaml
+++ b/ets2panda/util/diagnostic/syntax.yaml
@@ -242,6 +242,11 @@ syntax:
   id: 81515
   message: "Constructor signatures are not supported in interfaces, use methods instead!"
 
+- name: ERROR_ARKTS_NO_IN_OPERATOR
+  id: 105822
+  message: "'in' operator is not supported. Use 'instanceof' operator to check whether an object is the instance of a class
+    that contains the necessary class member."
+
 - name: ERROR_ARKTS_NO_OBJ_LITERAL_TO_DECL_TYPE
   id: 177354
   message: "Using object literals to declare types in place is not supported. Please declare types and interfaces explicitly!"