diff --git a/libraries/AP_HAL/Util.h b/libraries/AP_HAL/Util.h
index 4ae916a5ca..5e101cd7da 100644
--- a/libraries/AP_HAL/Util.h
+++ b/libraries/AP_HAL/Util.h
@@ -42,7 +42,7 @@ public:
     // commands
     virtual bool run_debug_shell(AP_HAL::BetterStream *stream) = 0;
 
-    enum safety_state {
+    enum safety_state : uint8_t {
         SAFETY_NONE, SAFETY_DISARMED, SAFETY_ARMED
     };
 
@@ -55,24 +55,25 @@ public:
     struct PersistentData {
         float roll_rad, pitch_rad, yaw_rad; // attitude
         int32_t home_lat, home_lon, home_alt_cm; // home position
-        bool armed; // true if vehicle was armed
-        enum safety_state safety_state;
+        uint32_t fault_addr;
+        uint32_t fault_icsr;
+        uint32_t fault_lr;
         uint32_t internal_errors;
         uint32_t internal_error_count;
+        uint32_t spi_count;
+        uint32_t i2c_count;
+        uint32_t i2c_isr_count;
         uint16_t waypoint_num;
-        int8_t scheduler_task;
         uint16_t last_mavlink_msgid;
         uint16_t last_mavlink_cmd;
         uint16_t semaphore_line;
-        uint32_t spi_count;
-        uint32_t i2c_count;
-        uint32_t i2c_isr_count;
         uint16_t fault_line;
         uint8_t fault_type;
         uint8_t fault_thd_prio;
-        uint32_t fault_addr;
-        uint32_t fault_icsr;
-        uint32_t fault_lr;
+        char thread_name4[4];
+        int8_t scheduler_task;
+        bool armed; // true if vehicle was armed
+        enum safety_state safety_state;
     };
     struct PersistentData persistent_data;
     // last_persistent_data is only filled in if we've suffered a watchdog reset