diff --git a/gd/l2cap/fcs.h b/gd/l2cap/fcs.h
new file mode 100644
index 0000000..42dd7dc
--- /dev/null
+++ b/gd/l2cap/fcs.h
@@ -0,0 +1,38 @@
+/*
+ * Copyright 2019 The Android Open Source Project
+ *
+ * Licensed 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.
+ */
+
+#pragma once
+
+#include <cstdint>
+
+namespace bluetooth {
+namespace l2cap {
+
+// Frame Check Sequence from the L2CAP spec.
+class Fcs {
+ public:
+  static void Initialize(Fcs& s);
+
+  static void AddByte(Fcs& s, uint8_t byte);
+
+  static uint16_t GetChecksum(const Fcs& s);
+
+ private:
+  uint16_t crc;
+};
+
+}  // namespace l2cap
+}  // namespace bluetooth