diff --git a/libraries/AP_HAL/SIMState.cpp b/libraries/AP_HAL/SIMState.cpp
index f5c4783422..08feffde66 100644
--- a/libraries/AP_HAL/SIMState.cpp
+++ b/libraries/AP_HAL/SIMState.cpp
@@ -266,7 +266,6 @@ void SIMState::fdm_input_local(void)
 
     set_height_agl();
 
-    _synthetic_clock_mode = true;
     _update_count++;
 }
 
diff --git a/libraries/AP_HAL/SIMState.h b/libraries/AP_HAL/SIMState.h
index f434347571..0d2334c68c 100644
--- a/libraries/AP_HAL/SIMState.h
+++ b/libraries/AP_HAL/SIMState.h
@@ -99,8 +99,6 @@ private:
     uint16_t _irlock_port;
     float _current;
 
-    bool _synthetic_clock_mode;
-
     bool _use_rtscts;
     bool _use_fg_view;