diff --git a/static_core/plugins/ets/runtime/ets_coroutine.cpp b/static_core/plugins/ets/runtime/ets_coroutine.cpp
index 151c85498a2fe38f262aec6148d9376fbd16b0f3..84da35c787734f78c4d27f07cf241f0ab0e365cc 100644
--- a/static_core/plugins/ets/runtime/ets_coroutine.cpp
+++ b/static_core/plugins/ets/runtime/ets_coroutine.cpp
@@ -70,6 +70,7 @@ void EtsCoroutine::Initialize()
         // initialization in MT ManagedThread ctor and EtsCoroutine::Initialize
         auto *linkExt = GetPandaVM()->GetClassLinker()->GetEtsClassLinkerExtension();
         SetStringClassPtr(linkExt->GetClassRoot(ClassRoot::STRING));
+        SetBaseStringClassPtr(linkExt->GetClassRoot(ClassRoot::BASE_STRING));
         SetArrayU16ClassPtr(linkExt->GetClassRoot(ClassRoot::ARRAY_U16));
         SetArrayU8ClassPtr(linkExt->GetClassRoot(ClassRoot::ARRAY_U8));
     }
diff --git a/static_core/plugins/ets/runtime/ets_vtable_builder.cpp b/static_core/plugins/ets/runtime/ets_vtable_builder.cpp
index 81ffd11fd466b1491585aea8f836aa8cd59dcacd..a320ba1e3dbfb6724d3426d0a836321d74dab293 100644
--- a/static_core/plugins/ets/runtime/ets_vtable_builder.cpp
+++ b/static_core/plugins/ets/runtime/ets_vtable_builder.cpp
@@ -139,6 +139,7 @@ static bool RefExtendsOrImplements(const ClassLinkerContext *ctx, RefTypeLink su
         return false;
     }
     panda_file::ClassDataAccessor const &superCDA = superCDAOpt.value();
+    // what about this?
     if (superCDA.IsFinal()) {
         return false;
     }
diff --git a/static_core/plugins/ets/runtime/intrinsics/std_core_Type.cpp b/static_core/plugins/ets/runtime/intrinsics/std_core_Type.cpp
index 71b2f7c3dc1788c9b6b08a128ee1b2fc39cf3ced..3b656c302ccc62ab96fab7a7a2435c1064e6197c 100644
--- a/static_core/plugins/ets/runtime/intrinsics/std_core_Type.cpp
+++ b/static_core/plugins/ets/runtime/intrinsics/std_core_Type.cpp
@@ -195,7 +195,7 @@ EtsString *TypeAPIGetUndefinedTypeDescriptor()
 EtsInt TypeAPIGetClassAttributes(EtsClass *cls)
 {
     uint32_t attrs = 0;
-    attrs |= (cls->IsFinal()) ? static_cast<uint32_t>(EtsTypeAPIAttributes::FINAL) : 0U;
+    attrs |= (cls->IsNotExtensible()) ? static_cast<uint32_t>(EtsTypeAPIAttributes::FINAL) : 0U;
 
     return static_cast<EtsInt>(attrs);
 }
diff --git a/static_core/plugins/ets/runtime/types/ets_class.h b/static_core/plugins/ets/runtime/types/ets_class.h
index 0c4b44f89c1aa1e38b05e754388126eaf73b7214..97e0ef7ed3101e7d35f86ccf98ad63d41e554a44 100644
--- a/static_core/plugins/ets/runtime/types/ets_class.h
+++ b/static_core/plugins/ets/runtime/types/ets_class.h
@@ -196,6 +196,11 @@ public:
         return GetRuntimeClass()->IsFinal();
     }
 
+    bool IsNotExtensible() const
+    {
+        return GetRuntimeClass()->IsNotExtensible();
+    }
+
     bool IsAnnotation() const
     {
         return GetRuntimeClass()->IsAnnotation();
diff --git a/static_core/runtime/include/class.h b/static_core/runtime/include/class.h
index a6121da5975ae474ead8522102d18625d9b97725..476809425b68fa1d4ac5b34787d93a63df74e14e 100644
--- a/static_core/runtime/include/class.h
+++ b/static_core/runtime/include/class.h
@@ -26,6 +26,7 @@
 #include "runtime/include/field.h"
 #include "runtime/include/itable.h"
 #include "runtime/include/method.h"
+#include "runtime/include/managed_thread.h"
 #include "libpandabase/macros.h"
 
 namespace ark {
@@ -290,6 +291,15 @@ public:
         return (accessFlags_ & ACC_FINAL) != 0;
     }
 
+    bool IsNotExtensible() const
+    {
+        auto baseStringKls = ManagedThread::GetCurrent()->GetBaseStringClassPtr();
+        if (this != baseStringKls) {
+            return this->IsFinal();
+        }
+        return baseStringKls == ManagedThread::GetCurrent()->GetStringClassPtr();
+    }
+
     bool IsAnnotation() const
     {
         return (accessFlags_ & ACC_ANNOTATION) != 0;
diff --git a/static_core/runtime/include/managed_thread.h b/static_core/runtime/include/managed_thread.h
index 2278a385abd79c3b2c5b997e74be4db7dfeb65d0..820ae542011b8bcbd81c756d7d6b4067f80ab369 100644
--- a/static_core/runtime/include/managed_thread.h
+++ b/static_core/runtime/include/managed_thread.h
@@ -191,6 +191,19 @@ public:
     {
         stringClassPtr_ = p;
     }
+    Class *GetStringClassPtr()
+    {
+        return static_cast<Class *>(stringClassPtr_);
+    }
+
+    void SetBaseStringClassPtr(void *p)
+    {
+        baseStringClassPtr_ = p;
+    }
+    Class *GetBaseStringClassPtr()
+    {
+        return static_cast<Class *>(baseStringClassPtr_);
+    }
 
     void SetArrayU8ClassPtr(void *p)
     {
diff --git a/static_core/runtime/include/thread.h b/static_core/runtime/include/thread.h
index 174784d30319f270af92fa1ebe4819bdcec32451..92d912dac4a7cff988b317468613ba6b51312c1f 100644
--- a/static_core/runtime/include/thread.h
+++ b/static_core/runtime/include/thread.h
@@ -338,6 +338,7 @@ protected:
     void *postWrbOneObject_ {nullptr};
     // keeps IRtoC GC PostWrb impl for storing two objects
     void *postWrbTwoObjects_ {nullptr};
+    void *baseStringClassPtr_ {nullptr};    // ClassRoot::STRING
     void *stringClassPtr_ {nullptr};    // ClassRoot::STRING
     void *arrayU16ClassPtr_ {nullptr};  // ClassRoot::ARRAY_U16
     void *arrayU8ClassPtr_ {nullptr};   // ClassRoot::ARRAY_U8
diff --git a/static_core/runtime/runtime.cpp b/static_core/runtime/runtime.cpp
index 09436a660dbbe71f8cc78f9b6f399e90b52f4169..59c52e80b82ce9350dca4646d4353b9693064ddf 100644
--- a/static_core/runtime/runtime.cpp
+++ b/static_core/runtime/runtime.cpp
@@ -890,6 +890,7 @@ void Runtime::SetThreadClassPointers()
     auto ext = GetClassLinker()->GetExtension(GetLanguageContext(GetRuntimeType()));
     if (ext != nullptr) {
         thread->SetStringClassPtr(ext->GetClassRoot(ClassRoot::STRING));
+        thread->SetBaseStringClassPtr(ext->GetClassRoot(ClassRoot::BASE_STRING));
         thread->SetArrayU16ClassPtr(ext->GetClassRoot(ClassRoot::ARRAY_U16));
         thread->SetArrayU8ClassPtr(ext->GetClassRoot(ClassRoot::ARRAY_U8));
     }