Check for the submodule

QGCExternalLibs.pri

@@ -107,7 +107,9 @@ else {
 
 # Then we add the proper include paths dependent on the dialect.
 INCLUDEPATH += $$MAVLINKPATH
-!isEmpty(MAVLINK_CONF) {
+
+exists($$MAVLINKPATH/common) {
+    !isEmpty(MAVLINK_CONF) {
         count(MAVLINK_CONF, 1) {
             exists($$MAVLINKPATH/$$MAVLINK_CONF) {
                 INCLUDEPATH += $$MAVLINKPATH/$$MAVLINK_CONF
@@ -118,9 +120,12 @@ INCLUDEPATH += $$MAVLINKPATH
         } else {
             error(Only a single mavlink dialect can be specified in MAVLINK_CONF)
         }
-} else {
+    } else {
         warning("No MAVLink dialect specified, only common messages supported.")
         INCLUDEPATH += $$MAVLINKPATH/common
+    }
+} else {
+    error($$sprintf("MAVLink folder does not exist at '%1'! Run 'git submodule init && git submodule update' on the command line.",$$MAVLINKPATH_REL))
 }
 
 #