diff --git a/src/modules/mavlink/mavlink_receiver.cpp b/src/modules/mavlink/mavlink_receiver.cpp
index 29f299f918..c4f1cbceec 100644
--- a/src/modules/mavlink/mavlink_receiver.cpp
+++ b/src/modules/mavlink/mavlink_receiver.cpp
@@ -1797,13 +1797,15 @@ MavlinkReceiver::receive_thread(void *arg)
 	while (!_mavlink->_task_should_exit) {
 		if (poll(&fds[0], 1, timeout) > 0) {
 			if (_mavlink->get_protocol() == SERIAL) {
+
+				/*
+				 * to avoid reading very small chunks wait for data before reading
+				 * this is designed to target ~30 bytes at a time
+				 */
+				const unsigned character_count = 20;
+
 				/* non-blocking read. read may return negative values */
-				if ((nread = ::read(uart_fd, buf, sizeof(buf))) < (ssize_t)sizeof(buf)) {
-					/*
-					 * to avoid reading very small chunks wait for data before reading
-					 * this is designed to target ~30 bytes at a time
-					 */
-					const unsigned character_count = 20;
+				if ((nread = ::read(uart_fd, buf, sizeof(buf))) < (ssize_t)character_count) {
 					unsigned sleeptime = (1.0f / (_mavlink->get_baudrate() / 10)) * character_count * 1000000;
 					usleep(sleeptime);
 				}