diff --git a/libraries/GCS_MAVLink/GCS.h b/libraries/GCS_MAVLink/GCS.h
index e3d0461976..886d1f72a4 100644
--- a/libraries/GCS_MAVLink/GCS.h
+++ b/libraries/GCS_MAVLink/GCS.h
@@ -75,6 +75,12 @@ void gcs_out_of_space_to_send(mavlink_channel_t chan);
 // scope.
 #define CHECK_PAYLOAD_SIZE2(id) if (!HAVE_PAYLOAD_SPACE(chan, id)) return false
 
+// CHECK_PAYLOAD_SIZE2_VOID - macro which inserts code which will
+// immediately return from the current (void) function if there is no
+// room to fit the mavlink message with id id on the mavlink output
+// channel "chan".
+#define CHECK_PAYLOAD_SIZE2_VOID(chan, id) if (!HAVE_PAYLOAD_SPACE(chan, id)) return
+
 // convenience macros for defining which ap_message ids are in which streams:
 #define MAV_STREAM_ENTRY(stream_name)           \
     {                                           \
@@ -170,6 +176,7 @@ public:
     void send_mission_ack(const mavlink_message_t &msg,
                           MAV_MISSION_TYPE mission_type,
                           MAV_MISSION_RESULT result) const {
+        CHECK_PAYLOAD_SIZE2_VOID(chan, MISSION_ACK);
         mavlink_msg_mission_ack_send(chan,
                                      msg.sysid,
                                      msg.compid,
diff --git a/libraries/GCS_MAVLink/MissionItemProtocol.cpp b/libraries/GCS_MAVLink/MissionItemProtocol.cpp
index 5792adc9f1..b90cc3b166 100644
--- a/libraries/GCS_MAVLink/MissionItemProtocol.cpp
+++ b/libraries/GCS_MAVLink/MissionItemProtocol.cpp
@@ -111,6 +111,7 @@ void MissionItemProtocol::handle_mission_request_list(
 
     // reply with number of commands in the mission.  The GCS will
     // then request each command separately
+    CHECK_PAYLOAD_SIZE2_VOID(_link.get_chan(), MISSION_COUNT);
     mavlink_msg_mission_count_send(_link.get_chan(),
                                    msg.sysid,
                                    msg.compid,
@@ -148,6 +149,7 @@ void MissionItemProtocol::handle_mission_request_int(const GCS_MAVLINK &_link,
         return;
     }
 
+    CHECK_PAYLOAD_SIZE2_VOID(_link.get_chan(), MISSION_ITEM_INT);
     _link.send_message(MAVLINK_MSG_ID_MISSION_ITEM_INT, (const char*)&ret_packet);
 }
 
@@ -186,6 +188,7 @@ void MissionItemProtocol::handle_mission_request(const GCS_MAVLINK &_link,
         return;
     }
 
+    CHECK_PAYLOAD_SIZE2_VOID(_link.get_chan(), MISSION_ITEM_INT);
     _link.send_message(MAVLINK_MSG_ID_MISSION_ITEM, (const char*)&ret_packet);
 }
 
@@ -293,6 +296,7 @@ void MissionItemProtocol::send_mission_ack(const GCS_MAVLINK &_link,
                                            const mavlink_message_t &msg,
                                            MAV_MISSION_RESULT result) const
 {
+    CHECK_PAYLOAD_SIZE2_VOID(_link.get_chan(), MISSION_ACK);
     mavlink_msg_mission_ack_send(_link.get_chan(),
                                  msg.sysid,
                                  msg.compid,
@@ -316,6 +320,7 @@ void MissionItemProtocol::queued_request_send()
         INTERNAL_ERROR(AP_InternalError::error_t::gcs_bad_missionprotocol_link);
         return;
     }
+    CHECK_PAYLOAD_SIZE2_VOID(link->get_chan(), MISSION_REQUEST);
     mavlink_msg_mission_request_send(
         link->get_chan(),
         dest_sysid,
@@ -340,11 +345,14 @@ void MissionItemProtocol::update()
     if (tnow - timelast_receive_ms > upload_timeout_ms) {
         receiving = false;
         timeout();
-        mavlink_msg_mission_ack_send(link->get_chan(),
-                                     dest_sysid,
-                                     dest_compid,
-                                     MAV_MISSION_OPERATION_CANCELLED,
-                                     mission_type());
+        const mavlink_channel_t chan = link->get_chan();
+        if (HAVE_PAYLOAD_SPACE(chan, MISSION_ACK)) {
+            mavlink_msg_mission_ack_send(chan,
+                                         dest_sysid,
+                                         dest_compid,
+                                         MAV_MISSION_OPERATION_CANCELLED,
+                                         mission_type());
+        }
         link = nullptr;
         free_upload_resources();
         return;
diff --git a/libraries/GCS_MAVLink/MissionItemProtocol_Waypoints.cpp b/libraries/GCS_MAVLink/MissionItemProtocol_Waypoints.cpp
index e707a1e286..6878ae92bb 100644
--- a/libraries/GCS_MAVLink/MissionItemProtocol_Waypoints.cpp
+++ b/libraries/GCS_MAVLink/MissionItemProtocol_Waypoints.cpp
@@ -65,11 +65,14 @@ MAV_MISSION_RESULT MissionItemProtocol_Waypoints::get_item(const GCS_MAVLINK &_l
     if (packet.seq != 0 && // always allow HOME to be read
         packet.seq >= mission.num_commands()) {
         // try to educate the GCS on the actual size of the mission:
-        mavlink_msg_mission_count_send(_link.get_chan(),
-                                       msg.sysid,
-                                       msg.compid,
-                                       mission.num_commands(),
-                                       MAV_MISSION_TYPE_MISSION);
+        const mavlink_channel_t chan = _link.get_chan();
+        if (HAVE_PAYLOAD_SPACE(chan, MISSION_COUNT)) {
+            mavlink_msg_mission_count_send(chan,
+                                           msg.sysid,
+                                           msg.compid,
+                                           mission.num_commands(),
+                                           MAV_MISSION_TYPE_MISSION);
+        }
         return MAV_MISSION_ERROR;
     }