diff --git a/src/qml/jsruntime/qv4functionobject.cpp b/src/qml/jsruntime/qv4functionobject.cpp
index b2d89220ea..e9431ed25e 100644
--- a/src/qml/jsruntime/qv4functionobject.cpp
+++ b/src/qml/jsruntime/qv4functionobject.cpp
@@ -131,7 +131,7 @@ void FunctionObject::init(String *n, bool createProto)
     }
 
     if (n)
-        defineReadonlyProperty(s.engine->id_name(), *n);
+        defineReadonlyConfigurableProperty(s.engine->id_name(), *n);
 }
 
 ReturnedValue FunctionObject::name() const
@@ -258,10 +258,10 @@ void FunctionPrototype::init(ExecutionEngine *engine, Object *ctor)
     Scope scope(engine);
     ScopedObject o(scope);
 
-    ctor->defineReadonlyProperty(engine->id_length(), Primitive::fromInt32(1));
+    ctor->defineReadonlyConfigurableProperty(engine->id_length(), Primitive::fromInt32(1));
     ctor->defineReadonlyProperty(engine->id_prototype(), (o = this));
 
-    defineReadonlyProperty(engine->id_length(), Primitive::fromInt32(0));
+    defineReadonlyConfigurableProperty(engine->id_length(), Primitive::fromInt32(0));
     defineDefaultProperty(QStringLiteral("constructor"), (o = ctor));
     defineDefaultProperty(engine->id_toString(), method_toString, 0);
     defineDefaultProperty(QStringLiteral("apply"), method_apply, 2);
@@ -557,7 +557,7 @@ void Heap::BoundFunction::init(QV4::ExecutionContext *scope, QV4::FunctionObject
         len -= boundArgs->size();
     if (len < 0)
         len = 0;
-    f->defineReadonlyProperty(s.engine->id_length(), Primitive::fromInt32(len));
+    f->defineReadonlyConfigurableProperty(s.engine->id_length(), Primitive::fromInt32(len));
 
     ScopedProperty pd(s);
     pd->value = s.engine->thrower();
diff --git a/src/qml/jsruntime/qv4global_p.h b/src/qml/jsruntime/qv4global_p.h
index 66861bf697..b0d14fc2b4 100644
--- a/src/qml/jsruntime/qv4global_p.h
+++ b/src/qml/jsruntime/qv4global_p.h
@@ -258,6 +258,7 @@ enum PropertyFlag {
     Attr_NotEnumerable = 0x4,
     Attr_NotConfigurable = 0x8,
     Attr_ReadOnly = Attr_NotWritable|Attr_NotEnumerable|Attr_NotConfigurable,
+    Attr_ReadOnly_ButConfigurable = Attr_NotWritable|Attr_NotEnumerable,
     Attr_Invalid = 0xff
 };
 
diff --git a/src/qml/jsruntime/qv4object.cpp b/src/qml/jsruntime/qv4object.cpp
index 2f664c6398..59195fc11e 100644
--- a/src/qml/jsruntime/qv4object.cpp
+++ b/src/qml/jsruntime/qv4object.cpp
@@ -162,7 +162,7 @@ void Object::defineDefaultProperty(const QString &name, ReturnedValue (*code)(Ca
     ScopedString s(scope, e->newIdentifier(name));
     ExecutionContext *global = e->rootContext();
     ScopedFunctionObject function(scope, BuiltinFunction::create(global, s, code));
-    function->defineReadonlyProperty(e->id_length(), Primitive::fromInt32(argumentCount));
+    function->defineReadonlyConfigurableProperty(e->id_length(), Primitive::fromInt32(argumentCount));
     defineDefaultProperty(s, function);
 }
 
@@ -173,7 +173,7 @@ void Object::defineDefaultProperty(const QString &name, void (*code)(const Built
     ScopedString s(scope, e->newIdentifier(name));
     ExecutionContext *global = e->rootContext();
     ScopedFunctionObject function(scope, BuiltinFunction::create(global, s, code));
-    function->defineReadonlyProperty(e->id_length(), Primitive::fromInt32(argumentCount));
+    function->defineReadonlyConfigurableProperty(e->id_length(), Primitive::fromInt32(argumentCount));
     defineDefaultProperty(s, function);
 }
 
@@ -183,7 +183,7 @@ void Object::defineDefaultProperty(String *name, ReturnedValue (*code)(CallConte
     Scope scope(e);
     ExecutionContext *global = e->rootContext();
     ScopedFunctionObject function(scope, BuiltinFunction::create(global, name, code));
-    function->defineReadonlyProperty(e->id_length(), Primitive::fromInt32(argumentCount));
+    function->defineReadonlyConfigurableProperty(e->id_length(), Primitive::fromInt32(argumentCount));
     defineDefaultProperty(name, function);
 }
 
@@ -193,7 +193,7 @@ void Object::defineDefaultProperty(String *name, void (*code)(const BuiltinFunct
     Scope scope(e);
     ExecutionContext *global = e->rootContext();
     ScopedFunctionObject function(scope, BuiltinFunction::create(global, name, code));
-    function->defineReadonlyProperty(e->id_length(), Primitive::fromInt32(argumentCount));
+    function->defineReadonlyConfigurableProperty(e->id_length(), Primitive::fromInt32(argumentCount));
     defineDefaultProperty(name, function);
 }
 
@@ -250,6 +250,19 @@ void Object::defineReadonlyProperty(String *name, const Value &value)
     insertMember(name, value, Attr_ReadOnly);
 }
 
+void Object::defineReadonlyConfigurableProperty(const QString &name, const Value &value)
+{
+    QV4::ExecutionEngine *e = engine();
+    Scope scope(e);
+    ScopedString s(scope, e->newIdentifier(name));
+    defineReadonlyConfigurableProperty(s, value);
+}
+
+void Object::defineReadonlyConfigurableProperty(String *name, const Value &value)
+{
+    insertMember(name, value, Attr_ReadOnly_ButConfigurable);
+}
+
 void Object::markObjects(Heap::Base *that, ExecutionEngine *e)
 {
     Heap::Object *o = static_cast<Heap::Object *>(that);
diff --git a/src/qml/jsruntime/qv4object_p.h b/src/qml/jsruntime/qv4object_p.h
index 6a543ae1a8..a54e09cdb2 100644
--- a/src/qml/jsruntime/qv4object_p.h
+++ b/src/qml/jsruntime/qv4object_p.h
@@ -253,6 +253,10 @@ struct Q_QML_EXPORT Object: Managed {
     void defineReadonlyProperty(const QString &name, const Value &value);
     void defineReadonlyProperty(String *name, const Value &value);
 
+    /* Fixed: Writable: false, Enumerable: false, Configurable: true */
+    void defineReadonlyConfigurableProperty(const QString &name, const Value &value);
+    void defineReadonlyConfigurableProperty(String *name, const Value &value);
+
     void insertMember(String *s, const Value &v, PropertyAttributes attributes = Attr_Data) {
         Scope scope(engine());
         ScopedProperty p(scope);
diff --git a/tests/manual/v4/TestExpectations b/tests/manual/v4/TestExpectations
index 49f107452a..abb155d9d2 100644
--- a/tests/manual/v4/TestExpectations
+++ b/tests/manual/v4/TestExpectations
@@ -29,3 +29,101 @@ Sbp_12.5_A9_T3 failing
 Sbp_12.6.1_A13_T3 failing
 Sbp_12.6.2_A13_T3 failing
 Sbp_12.6.4_A13_T3 failing
+
+# function length attributes are configurable in es6
+S15.1.2.2_A9.2 failing
+S15.1.3.1_A5.2 failing
+S15.1.3.2_A5.2 failing
+S15.1.3.3_A5.2 failing
+S15.1.2.3_A7.2 failing
+S15.1.2.4_A2.2 failing
+S15.1.2.5_A2.2 failing
+S15.1.3.4_A5.2 failing
+15.2.3.3-4-186 failing
+S15.2.4.2_A9 failing
+S15.2.4.3_A9 failing
+S15.2.4.4_A9 failing
+S15.2.4.5_A9 failing
+S15.2.4.6_A9 failing
+S15.2.4.7_A9 failing
+15.3.3.2-1 failing
+15.4.4.2_A4.2
+S15.3.4.2_A9 failing
+S15.3.4.3_A9 failing
+S15.3.4.4_A9 failing
+15.3.4.5-15-2 failing
+S15.4.4.2_A4.2 failing
+S15.4.4.3_A4.2 failing
+S15.4.4.4_A4.2 failing
+S15.4.4.5_A6.2 failing
+S15.4.4.6_A5.2 failing
+S15.4.4.7_A6.2 failing
+S15.4.4.8_A5.2 failing
+S15.4.4.9_A5.2 failing
+S15.4.4.10_A5.2 failing
+S15.4.4.11_A7.2 failing
+S15.4.4.12_A5.2 failing
+S15.4.4.13_A5.2 failing
+S15.5.4.10_A9 failing
+S15.5.4.11_A9 failing
+S15.5.4.12_A9 failing
+S15.5.4.13_A9 failing
+S15.5.4.14_A9 failing
+S15.5.4.15_A9 failing
+S15.5.4.16_A9 failing
+S15.5.4.17_A9 failing
+S15.5.4.18_A9 failing
+S15.5.4.19_A9 failing
+S15.5.4.4_A9 failing
+S15.5.4.5_A9 failing
+S15.5.4.6_A9 failing
+S15.5.4.7_A9 failing
+S15.5.4.8_A9 failing
+S15.5.4.9_A9 failing
+S15.9.4.2_A3_T2 failing
+S15.9.4.3_A3_T2 failing
+S15.9.5.2_A3_T2 failing
+S15.9.5.3_A3_T2 failing
+S15.9.5.4_A3_T2 failing
+S15.9.5.5_A3_T2 failing
+S15.9.5.10_A3_T2 failing
+S15.9.5.11_A3_T2 failing
+S15.9.5.12_A3_T2 failing
+S15.9.5.13_A3_T2 failing
+S15.9.5.14_A3_T2 failing
+S15.9.5.15_A3_T2 failing
+S15.9.5.16_A3_T2 failing
+S15.9.5.17_A3_T2 failing
+S15.9.5.18_A3_T2 failing
+S15.9.5.19_A3_T2 failing
+S15.9.5.20_A3_T2 failing
+S15.9.5.21_A3_T2 failing
+S15.9.5.22_A3_T2 failing
+S15.9.5.23_A3_T2 failing
+S15.9.5.24_A3_T2 failing
+S15.9.5.25_A3_T2 failing
+S15.9.5.26_A3_T2 failing
+S15.9.5.27_A3_T2 failing
+S15.9.5.28_A3_T2 failing
+S15.9.5.29_A3_T2 failing
+S15.9.5.30_A3_T2 failing
+S15.9.5.31_A3_T2 failing
+S15.9.5.32_A3_T2 failing
+S15.9.5.33_A3_T2 failing
+S15.9.5.34_A3_T2 failing
+S15.9.5.35_A3_T2 failing
+S15.9.5.36_A3_T2 failing
+S15.9.5.37_A3_T2 failing
+S15.9.5.38_A3_T2 failing
+S15.9.5.39_A3_T2 failing
+S15.9.5.40_A3_T2 failing
+S15.9.5.41_A3_T2 failing
+S15.9.5.42_A3_T2 failing
+S15.9.5.6_A3_T2 failing
+S15.9.5.7_A3_T2 failing
+S15.9.5.8_A3_T2 failing
+S15.9.5.9_A3_T2 failing
+S15.10.6.2_A9 failing
+S15.10.6.3_A9 failing
+S15.10.6.4_A9 failing
+