diff --git a/src/google/protobuf/message_lite.cc b/src/google/protobuf/message_lite.cc
index 0c9ca99..c37e661 100644
--- a/src/google/protobuf/message_lite.cc
+++ b/src/google/protobuf/message_lite.cc
@@ -86,16 +86,6 @@
   data->merge_to_from(*this, other);
 }
 
-void MessageLite::MergeFromWithClassData(const MessageLite& other,
-                                         const internal::ClassData* data) {
-  ABSL_DCHECK(data != nullptr);
-  ABSL_DCHECK(GetClassData() == data && other.GetClassData() == data)
-      << "Invalid call to " << __func__ << ": this=" << GetTypeName()
-      << " other=" << other.GetTypeName()
-      << " data=" << data->prototype->GetTypeName();
-  data->merge_to_from(*this, other);
-}
-
 MessageLite* MessageLite::New(Arena* arena) const {
   auto* data = GetClassData();
   // The `instance->New()` expression requires using the actual instance
diff --git a/src/google/protobuf/message_lite.h b/src/google/protobuf/message_lite.h
index a568dd6..25264ef 100644
--- a/src/google/protobuf/message_lite.h
+++ b/src/google/protobuf/message_lite.h
@@ -932,6 +932,21 @@
         CopyConstruct(arena, reinterpret_cast<const MessageLite&>(from)));
   }
 
+  // `CheckTypeAndMergeFrom()` and should be preferred by friended internal
+  // callers that have the right `ClassData` handy.
+  // REQUIRES: Both `this` and `other` are the exact same class as represented
+  // by `data`. If there is a mismatch, CHECK-fails in debug builds or causes UB
+  // in release builds (probably a crash).
+  PROTOBUF_ALWAYS_INLINE void MergeFromWithClassData(
+      const MessageLite& other, const internal::ClassData* data) {
+    ABSL_DCHECK(data != nullptr);
+    ABSL_DCHECK(GetClassData() == data && other.GetClassData() == data)
+        << "Invalid call to " << __func__ << ": this=" << GetTypeName()
+        << " other=" << other.GetTypeName()
+        << " data=" << data->prototype->GetTypeName();
+    data->merge_to_from(*this, other);
+  }
+
   const internal::TcParseTableBase* GetTcParseTable() const {
     auto* data = GetClassData();
     ABSL_DCHECK(data != nullptr);
@@ -1123,15 +1138,7 @@
 
   void LogInitializationErrorMessage() const;
 
-  // Merges the contents of `other` into `this`. This is faster than
-  // `CheckTypeAndMergeFrom()` and should be preferred by friended internal
-  // callers that have the right `ClassData` handy.
-  // REQUIRES: Both `this` and `other` are the exact same class as represented
-  // by `data`. If there is a mismatch, CHECK-fails in debug builds or causes UB
-  // in release builds (probably a crash).
-  void MergeFromWithClassData(const MessageLite& other,
-                              const internal::ClassData* data);
-
+ private:
   bool MergeFromImpl(io::CodedInputStream* input, ParseFlags parse_flags);
 
   // Runs the destructor for this instance.