diff --git a/libs/surfaces/mackie/mackie_control_protocol.cc b/libs/surfaces/mackie/mackie_control_protocol.cc
index 0fd9743a7d..61225b309a 100644
--- a/libs/surfaces/mackie/mackie_control_protocol.cc
+++ b/libs/surfaces/mackie/mackie_control_protocol.cc
@@ -1133,7 +1133,17 @@ MackieControlProtocol::midi_input_handler (IOCondition ioc, MIDI::Port* port)
 
 	if (ioc & IO_IN) {
 
-		CrossThreadChannel::drain (port->selectable());
+		/* Devices using regular JACK MIDI ports will need to have
+		   the x-thread FIFO drained to avoid burning endless CPU.
+
+		   Devices using ipMIDI have port->selectable() as the same
+		   file descriptor that data arrives on, so doing this
+		   for them will simply throw all incoming data away.
+		*/
+
+		if (!_device_info.uses_ipmidi()) {
+			CrossThreadChannel::drain (port->selectable());
+		}
 
 		DEBUG_TRACE (DEBUG::MackieControl, string_compose ("data available on %1\n", port->name()));
 		framepos_t now = session->engine().frame_time();
diff --git a/libs/surfaces/mackie/surface.cc b/libs/surfaces/mackie/surface.cc
index 0cc0f02a77..0a5ea09e3e 100644
--- a/libs/surfaces/mackie/surface.cc
+++ b/libs/surfaces/mackie/surface.cc
@@ -409,9 +409,9 @@ Surface::handle_midi_sysex (MIDI::Parser &, MIDI::byte * raw_bytes, size_t count
 	 */
 
 	if (_stype == mcu) {
-		mackie_sysex_hdr[3] = bytes[4];
+		mackie_sysex_hdr[4] = bytes[4];
 	} else {
-		mackie_sysex_hdr_xt[3] = bytes[4];
+		mackie_sysex_hdr_xt[4] = bytes[4];
 	}
 
 	switch (bytes[5]) {