diff --git a/OSBindings/Mac/Clock Signal/Machine/CSMachine.mm b/OSBindings/Mac/Clock Signal/Machine/CSMachine.mm
index 3944bf37d..18f43f55b 100644
--- a/OSBindings/Mac/Clock Signal/Machine/CSMachine.mm	
+++ b/OSBindings/Mac/Clock Signal/Machine/CSMachine.mm	
@@ -723,7 +723,7 @@ struct ActivityObserver: public Activity::Observer {
 			// _syncTime = 0 is used here as a sentinel to mark that a sync time is known;
 			// this with the >= test ensures that no syncs are missed even if some sort of
 			// performance problem is afoot (e.g. I'm debugging).
-			if(self->_syncTime && timeNow >= self->_syncTime) {
+			if(self->_syncTime && timeNow >= self->_syncTime && self->_syncTime >= lastTime) {
 				splitAndSync = self->_isSyncLocking = self->_scanSynchroniser.can_synchronise(self->_machine->scan_producer()->get_scan_status(), self->_refreshPeriod);
 
 				// If the time window is being split, run up to the split, then check out machine speed, possibly