diff --git a/ArduSub/Log.cpp b/ArduSub/Log.cpp
index fd8aec5f61..7512ddd283 100644
--- a/ArduSub/Log.cpp
+++ b/ArduSub/Log.cpp
@@ -468,12 +468,17 @@ void Sub::Log_Write_Vehicle_Startup_Messages()
 // start a new log
 void Sub::start_logging()
 {
-    if (g.log_bitmask != 0) {
+    if (g.log_bitmask != 0 && !in_log_download) {
         if (!ap.logging_started) {
             ap.logging_started = true;
             DataFlash.set_mission(&mission);
             DataFlash.setVehicle_Startup_Log_Writer(FUNCTOR_BIND(&sub, &Sub::Log_Write_Vehicle_Startup_Messages, void));
             DataFlash.StartNewLog();
+        } else if (!DataFlash.logging_started()) {
+            hal.console->println("Starting new log");
+            // dataflash may have stopped logging - when we get_log_data,
+            // for example.  Try to restart:
+            DataFlash.StartNewLog();
         }
         // enable writes
         DataFlash.EnableWrites(true);
diff --git a/ArduSub/motors.cpp b/ArduSub/motors.cpp
index 1e6590784e..c0a73a46fe 100644
--- a/ArduSub/motors.cpp
+++ b/ArduSub/motors.cpp
@@ -12,6 +12,7 @@ void Sub::enable_motor_output()
 //  returns false if arming failed because of pre-arm checks, arming checks or a gyro calibration failure
 bool Sub::init_arm_motors(bool arming_from_gcs)
 {
+    start_logging();
     static bool in_arm_motors = false;
 
     // exit immediately if already in this function
@@ -27,6 +28,9 @@ bool Sub::init_arm_motors(bool arming_from_gcs)
         return false;
     }
 
+    // let dataflash know that we're armed (it may open logs e.g.)
+    DataFlash_Class::instance()->set_vehicle_armed(true);
+
     // disable cpu failsafe because initialising everything takes a while
     mainloop_failsafe_disable();
 
@@ -118,6 +122,7 @@ void Sub::init_disarm_motors()
     if (!DataFlash.log_while_disarmed()) {
         DataFlash.EnableWrites(false);
     }
+    DataFlash_Class::instance()->set_vehicle_armed(false);
 
     // disable gps velocity based centrefugal force compensation
     ahrs.set_correct_centrifugal(false);