diff --git a/android/hal-ipc-api.txt b/android/hal-ipc-api.txt
index 49d704e..70c451d 100644
--- a/android/hal-ipc-api.txt
+++ b/android/hal-ipc-api.txt
@@ -1421,6 +1421,12 @@ Android HAL name: "gatt" (BT_PROFILE_GATT_ID)
 		                     0x0a = Remote device down
 
 	Opcode 0x01 - Register Client command/response
+
+		Command parameters: Service UUID (16 octets)
+		Response parameters: <none>
+
+		In case of an error, the error response will be returned.
+
 	Opcode 0x02 - Unregister Client command/response
 	Opcode 0x03 - Scan command/response
 	Opcode 0x04 - Connect Device command/response
diff --git a/android/hal-msg.h b/android/hal-msg.h
index 094e112..350a75c 100644
--- a/android/hal-msg.h
+++ b/android/hal-msg.h
@@ -516,6 +516,13 @@ struct hal_cmd_handsfree_phone_state_change {
 	uint8_t number[0];
 } __attribute__((packed));
 
+/* GATT HAL API */
+
+#define HAL_OP_GATT_CLIENT_REGISTER		0x01
+struct hal_cmd_gatt_client_register {
+	uint8_t uuid[16];
+} __attribute__((packed));
+
 /* Notifications and confirmations */
 
 #define HAL_POWER_OFF			0x00