diff --git a/src/aio.c b/src/aio.c
index 8f7ec64..f2eb17b 100644
--- a/src/aio.c
+++ b/src/aio.c
@@ -58,10 +58,12 @@ static void aio_usb_release(libusb_device_handle *dev) {
 	libusb_release_interface(dev, 0);
 }
 
-static void aio_post(libusb_device_handle *dev, uint8_t *req, const int req_len, uint8_t *resp, const int resp_len) {
+static int aio_post(libusb_device_handle *dev, uint8_t *req, const int req_len, uint8_t *resp, const int resp_len) {
 	// applog(LOG_DBG, "writing to aio, %02x", req[0]);
-	libusb_bulk_transfer(dev, 0x01, req, req_len, nullptr, usb_timeout);
-	libusb_bulk_transfer(dev, 0x81, resp, resp_len, nullptr, usb_timeout);
+	int ret = 0;
+	ret += libusb_bulk_transfer(dev, 0x01, req, req_len, nullptr, usb_timeout);
+	ret += libusb_bulk_transfer(dev, 0x81, resp, resp_len, nullptr, usb_timeout);
+	return ret;
 }
 
 static float aio_get_water_temp(libusb_device_handle *dev) {
@@ -106,8 +108,9 @@ static void aio_set_fan_duty(libusb_device_handle *dev, const uint8_t *duty) {
 		req[2] = MIN(MAX(duty[i], 0), 100);
 		if (params.fans.fan_stop && req[2] <= params.fans.min_duty)
 			req[2] = 0;
-		aio_post(dev, req, sizeof(req), resp, buf_size);
-		last_duty = req[2];
+		const int ret = aio_post(dev, req, sizeof(req), resp, buf_size);
+		if (ret == 0)
+			last_duty = req[2];
 	}
 }