diff --git a/src/modules/mavlink/mavlink_main.cpp b/src/modules/mavlink/mavlink_main.cpp
index 9b2b14c2b6..057f957d9d 100644
--- a/src/modules/mavlink/mavlink_main.cpp
+++ b/src/modules/mavlink/mavlink_main.cpp
@@ -893,9 +893,9 @@ Mavlink::get_free_tx_buf()
 		return  1500;
 
 	} else {
-		// No FIONWRITE on Linux
+		// No FIONSPACE on Linux todo:use SIOCOUTQ  and queue size to emulate FIONSPACE
 #if !defined(__PX4_LINUX) && !defined(__PX4_DARWIN)
-		(void) ioctl(_uart_fd, FIONWRITE, (unsigned long)&buf_free);
+		(void) ioctl(_uart_fd, FIONSPACE, (unsigned long)&buf_free);
 #else
 		//Linux cp210x does not support TIOCOUTQ
 		buf_free = 256;
diff --git a/src/modules/syslink/syslink_bridge.cpp b/src/modules/syslink/syslink_bridge.cpp
index b4fddf4ab5..fbc828c6ec 100644
--- a/src/modules/syslink/syslink_bridge.cpp
+++ b/src/modules/syslink/syslink_bridge.cpp
@@ -136,12 +136,8 @@ SyslinkBridge::ioctl(struct file *filp, int cmd, unsigned long arg)
 	// All termios commands should be silently ignored as they are handled
 
 	switch (cmd) {
-#ifdef FIONSPACE
 
 	case FIONSPACE:
-#else
-	case FIONWRITE:
-#endif
 		*((int *) arg) = _link->_writebuffer.space() * CRTP_MAX_DATA_SIZE;
 		return 0;