diff --git a/jerry-core/ecma/builtin-objects/ecma-builtin-object.cpp b/jerry-core/ecma/builtin-objects/ecma-builtin-object.cpp
index c3a6d12530..d6f49b2738 100644
--- a/jerry-core/ecma/builtin-objects/ecma-builtin-object.cpp
+++ b/jerry-core/ecma/builtin-objects/ecma-builtin-object.cpp
@@ -176,10 +176,24 @@ ecma_builtin_object_object_freeze (ecma_value_t this_arg, /**< 'this' argument *
  *         Returned value must be freed with ecma_free_completion_value.
  */
 static ecma_completion_value_t
-ecma_builtin_object_object_prevent_extensions (ecma_value_t this_arg, /**< 'this' argument */
+ecma_builtin_object_object_prevent_extensions (ecma_value_t this_arg __attr_unused___, /**< 'this' argument */
                                                ecma_value_t arg) /**< routine's argument */
 {
-  ECMA_BUILTIN_CP_UNIMPLEMENTED (this_arg, arg);
+  ecma_completion_value_t ret_value = ecma_make_empty_completion_value ();
+
+  if (!ecma_is_value_object (arg))
+  {
+    ret_value = ecma_make_throw_obj_completion_value (ecma_new_standard_error (ECMA_ERROR_TYPE));
+  }
+  else
+  {
+    ecma_object_t *obj_p = ecma_get_object_from_value (arg);
+    ecma_set_object_extensible (obj_p, false);
+
+    ret_value = ecma_make_normal_completion_value (ecma_copy_value (arg, true));
+  }
+
+  return ret_value;
 } /* ecma_builtin_object_object_prevent_extensions */
 
 /**
@@ -224,10 +238,27 @@ ecma_builtin_object_object_is_frozen (ecma_value_t this_arg, /**< 'this' argumen
  *         Returned value must be freed with ecma_free_completion_value.
  */
 static ecma_completion_value_t
-ecma_builtin_object_object_is_extensible (ecma_value_t this_arg, /**< 'this' argument */
+ecma_builtin_object_object_is_extensible (ecma_value_t this_arg __attr_unused___, /**< 'this' argument */
                                           ecma_value_t arg) /**< routine's argument */
 {
-  ECMA_BUILTIN_CP_UNIMPLEMENTED (this_arg, arg);
+  ecma_completion_value_t ret_value = ecma_make_empty_completion_value ();
+
+  if (!ecma_is_value_object (arg))
+  {
+    ret_value = ecma_make_throw_obj_completion_value (ecma_new_standard_error (ECMA_ERROR_TYPE));
+  }
+  else
+  {
+    ecma_object_t *obj_p = ecma_get_object_from_value (arg);
+
+    bool extensible = ecma_get_object_extensible (obj_p);
+
+    ret_value = ecma_make_simple_completion_value (extensible
+                                                   ? ECMA_SIMPLE_VALUE_TRUE
+                                                   : ECMA_SIMPLE_VALUE_FALSE);
+  }
+
+  return ret_value;
 } /* ecma_builtin_object_object_is_extensible */
 
 /**
diff --git a/tests/jerry/object_is_extensible.js b/tests/jerry/object_is_extensible.js
new file mode 100644
index 0000000000..4d0e397aa0
--- /dev/null
+++ b/tests/jerry/object_is_extensible.js
@@ -0,0 +1,48 @@
+// Copyright 2015 Samsung Electronics Co., Ltd.
+// Copyright 2015 University of Szeged.
+//
+// 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.
+
+// New objects are extensible.
+var empty = {};
+assert (Object.isExtensible(empty) === true);
+
+// ...but that can be changed.
+Object.preventExtensions(empty);
+assert(Object.isExtensible(empty) === false);
+
+// Call on undefined should throw TypeError.
+try
+{
+    Object.isExtensible(undefined);
+    assert (false);
+} catch (e) {
+    assert (e instanceof TypeError);
+}
+
+try
+{
+    Object.preventExtensions(undefined);
+    assert (false);
+} catch (e) {
+    assert (e instanceof TypeError);
+}
+
+// The functions below are unimplemented.
+// Sealed objects are by definition non-extensible.
+// var sealed = Object.seal({});
+// assert(Object.isExtensible(sealed) === false);
+
+// Frozen objects are also by definition non-extensible.
+// var frozen = Object.freeze({});
+// assert(Object.isExtensible(frozen) === false);