diff --git a/libraries/AP_HAL/Scheduler.h b/libraries/AP_HAL/Scheduler.h
index 40202e9350..0344375158 100644
--- a/libraries/AP_HAL/Scheduler.h
+++ b/libraries/AP_HAL/Scheduler.h
@@ -61,5 +61,8 @@ public:
      */
     virtual void     stop_clock(uint64_t time_usec) {}
 
+    virtual bool     in_main_thread() const = 0;
+
     virtual void create_uavcan_thread() {};
+
 };