diff --git a/libraries/AP_HAL_SITL/Scheduler.cpp b/libraries/AP_HAL_SITL/Scheduler.cpp
index 12a77a8d0c..32eeebfa70 100644
--- a/libraries/AP_HAL_SITL/Scheduler.cpp
+++ b/libraries/AP_HAL_SITL/Scheduler.cpp
@@ -301,7 +301,7 @@ void Scheduler::_run_io_procs()
 void Scheduler::stop_clock(uint64_t time_usec)
 {
     _stopped_clock_usec = time_usec;
-    if (time_usec - _last_io_run > 10000) {
+    if (_sitlState->_sitl != nullptr && time_usec - _last_io_run > 10000) {
         _last_io_run = time_usec;
         _run_io_procs();
     }