diff --git a/src/Time/TimeManager.cxx b/src/Time/TimeManager.cxx
index e32827620..bb9c3693d 100644
--- a/src/Time/TimeManager.cxx
+++ b/src/Time/TimeManager.cxx
@@ -382,7 +382,12 @@ void TimeManager::computeTimeDeltasSimple(double& simDt, double& realDt)
 
 void TimeManager::computeTimeDeltas(double& simDt, double& realDt)
 {
-    if (_simpleTimeEnabled->getBoolValue()) {
+    bool simple_time = _simpleTimeEnabled->getBoolValue();
+    if (simple_time != _simpleTimeEnabledPrev) {
+        _simpleTimeEnabledPrev = simple_time;
+        _firstUpdate = true;
+    }
+    if (simple_time) {
         computeTimeDeltasSimple(simDt, realDt);
         return;
     }
diff --git a/src/Time/TimeManager.hxx b/src/Time/TimeManager.hxx
index 27f6948ec..f173e38bf 100644
--- a/src/Time/TimeManager.hxx
+++ b/src/Time/TimeManager.hxx
@@ -128,6 +128,7 @@ private:
     SGPropertyNode_ptr _modelHz;
     SGPropertyNode_ptr _timeDelta, _simTimeDelta;
     
+    bool    _simpleTimeEnabledPrev = false;
     SGPropertyNode_ptr _simpleTimeEnabled;
     SGPropertyNode_ptr _simpleTimeUtc;
     SGPropertyNode_ptr _simpleTimeFdm;