diff --git a/src/aio.c b/src/aio.c
index c62d4ae..be4df92 100644
--- a/src/aio.c
+++ b/src/aio.c
@@ -28,7 +28,7 @@ static enum aio_pump_mode_t aio_get_pump_mode(libusb_device_handle* aio) {
 }
 
 static void aio_get_fan_speed(libusb_device_handle* aio, uint16_t *speeds) {
-	uint8_t req[2] = {0x41};
+	uint8_t req[2] = {0x41}; // 2nd element is the fan id.
 	uint8_t resp[buf_size];
 
 	for (uint8_t i = 0; i < 2; i++) {