diff --git a/libraries/AP_Notify/ToneAlarm_Linux.h b/libraries/AP_Notify/ToneAlarm_Linux.h
index 293a1518b8..5211038305 100644
--- a/libraries/AP_Notify/ToneAlarm_Linux.h
+++ b/libraries/AP_Notify/ToneAlarm_Linux.h
@@ -40,12 +40,12 @@ private:
 
     /// tonealarm_type - bitmask of states we track
     struct tonealarm_type {
-        bool armed              : true;    // false = disarmed, true = armed
-        bool failsafe_battery   : true;    // true if battery failsafe
-        bool gps_glitching      : true;    // true if gps position is not good
-        bool failsafe_gps       : true;    // true if gps failsafe
-        bool arming_failed      : true;    // false = failing checks, true = passed
-        bool parachute_release  : true;    // true if parachute is being released
+        bool armed              : 1;    // false = disarmed, true = armed
+        bool failsafe_battery   : 1;    // true if battery failsafe
+        bool gps_glitching      : 1;    // true if gps position is not good
+        bool failsafe_gps       : 1;    // true if gps failsafe
+        bool arming_failed      : 1;    // false = failing checks, true = passed
+        bool parachute_release  : 1;    // true if parachute is being released
     } flags;
 };