diff --git a/src/google/protobuf/extension_set.cc b/src/google/protobuf/extension_set.cc
index e6a61e1a5f2b..00b2c4841717 100644
--- a/src/google/protobuf/extension_set.cc
+++ b/src/google/protobuf/extension_set.cc
@@ -1092,10 +1092,8 @@ void ExtensionSet::InternalExtensionMergeFromIntoUninitializedExtension(
     case WireFormatLite::CPPTYPE_MESSAGE: {
       if (other_extension.is_lazy) {
         dst_extension.ptr.lazymessage_value =
-            other_extension.ptr.lazymessage_value->New(arena_);
-        dst_extension.ptr.lazymessage_value->MergeFrom(
-            GetPrototypeForLazyMessage(extendee, number),
-            *other_extension.ptr.lazymessage_value, arena_, other_arena);
+            other_extension.ptr.lazymessage_value->Clone(
+                arena_, *other_extension.ptr.lazymessage_value, other_arena);
       } else {
         dst_extension.ptr.message_value =
             other_extension.ptr.message_value->New(arena_);
diff --git a/src/google/protobuf/extension_set.h b/src/google/protobuf/extension_set.h
index 1a3b606055f4..e7e407b66c11 100644
--- a/src/google/protobuf/extension_set.h
+++ b/src/google/protobuf/extension_set.h
@@ -624,7 +624,9 @@ class PROTOBUF_EXPORT ExtensionSet {
     LazyMessageExtension& operator=(const LazyMessageExtension&) = delete;
     virtual ~LazyMessageExtension() = default;
 
-    virtual LazyMessageExtension* New(Arena* arena) const = 0;
+    virtual LazyMessageExtension* Clone(Arena* arena,
+                                        const LazyMessageExtension& other,
+                                        Arena* other_arena) const = 0;
     virtual const MessageLite& GetMessage(const MessageLite& prototype,
                                           Arena* arena) const = 0;
     virtual const MessageLite& GetMessageIgnoreUnparsed(