diff --git a/jerry-core/ecma/builtin-objects/ecma-builtin-function-prototype.inc.h b/jerry-core/ecma/builtin-objects/ecma-builtin-function-prototype.inc.h
index 701fa3feb..340003cc4 100644
--- a/jerry-core/ecma/builtin-objects/ecma-builtin-function-prototype.inc.h
+++ b/jerry-core/ecma/builtin-objects/ecma-builtin-function-prototype.inc.h
@@ -52,7 +52,7 @@ OBJECT_VALUE (LIT_MAGIC_STRING_CONSTRUCTOR,
 // 15.3.4
 NUMBER_VALUE (LIT_MAGIC_STRING_LENGTH,
               0,
-              ECMA_PROPERTY_WRITABLE,
+              ECMA_PROPERTY_NOT_WRITABLE,
               ECMA_PROPERTY_NOT_ENUMERABLE,
               ECMA_PROPERTY_NOT_CONFIGURABLE)
 
diff --git a/tests/jerry/regression-test-issue-642.js b/tests/jerry/regression-test-issue-642.js
new file mode 100644
index 000000000..5d95fb208
--- /dev/null
+++ b/tests/jerry/regression-test-issue-642.js
@@ -0,0 +1,18 @@
+// 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.
+
+Function.prototype.length = function() {};
+Function.prototype.bind(0);
+assert (Function.prototype.length === 0);