diff --git a/src/google/protobuf/message.cc b/src/google/protobuf/message.cc
index eb81694daf..2cf07dbdf4 100644
--- a/src/google/protobuf/message.cc
+++ b/src/google/protobuf/message.cc
@@ -188,7 +188,13 @@ size_t Message::MaybeComputeUnknownFieldsSize(
 }
 
 size_t Message::SpaceUsedLong() const {
-  return GetReflection()->SpaceUsedLong(*this);
+  auto* reflection = GetReflection();
+  if (PROTOBUF_PREDICT_TRUE(reflection != nullptr)) {
+    return reflection->SpaceUsedLong(*this);
+  }
+  // The only case that does not have reflection is RawMessage.
+  return internal::DownCast<const internal::RawMessageBase&>(*this)
+      .SpaceUsedLong();
 }
 
 static std::string GetTypeNameImpl(const MessageLite& msg) {
diff --git a/src/google/protobuf/message.h b/src/google/protobuf/message.h
index 83ba793e93..47f41b89ec 100644
--- a/src/google/protobuf/message.h
+++ b/src/google/protobuf/message.h
@@ -286,8 +286,7 @@ class PROTOBUF_EXPORT Message : public MessageLite {
   void DiscardUnknownFields();
 
   // Computes (an estimate of) the total number of bytes currently used for
-  // storing the message in memory.  The default implementation calls the
-  // Reflection object's SpaceUsed() method.
+  // storing the message in memory.
   //
   // SpaceUsed() is noticeably slower than ByteSize(), as it is implemented
   // using reflection (rather than the generated code implementation for
@@ -297,7 +296,7 @@ class PROTOBUF_EXPORT Message : public MessageLite {
   // Note: The precise value of this method should never be depended on, and can
   // change substantially due to internal details.  In debug builds, this will
   // include a random fuzz factor to prevent these dependencies.
-  virtual size_t SpaceUsedLong() const;
+  size_t SpaceUsedLong() const;
 
   [[deprecated("Please use SpaceUsedLong() instead")]] int SpaceUsed() const {
     return internal::ToIntSize(SpaceUsedLong());
@@ -1573,6 +1572,12 @@ bool SplitFieldHasExtraIndirectionStatic(const FieldDescriptor* field) {
   return ret;
 }
 
+class RawMessageBase : public Message {
+ public:
+  using Message::Message;
+  virtual size_t SpaceUsedLong() const = 0;
+};
+
 }  // namespace internal
 
 template <typename Type>