diff --git a/ArduCopter/system.pde b/ArduCopter/system.pde
index af1bc6af88..df832abdbb 100644
--- a/ArduCopter/system.pde
+++ b/ArduCopter/system.pde
@@ -252,6 +252,10 @@ static void init_ardupilot()
         init_optflow();
     }
 
+#if INERTIAL_NAV_XY == ENABLED || INERTIAL_NAV_Z == ENABLED
+    // initialise inertial nav
+    inertial_nav.init();
+#endif
 
 // agmatthews USERHOOKS
 #ifdef USERHOOK_INIT