diff --git a/lib/rb/ext/protocol.c b/lib/rb/ext/protocol.c
index 207e78d..756f8b2 100644
--- a/lib/rb/ext/protocol.c
+++ b/lib/rb/ext/protocol.c
@@ -1,3 +1,22 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
 #include <ruby.h>
 #include <protocol.h>
 #include <stdbool.h>