diff --git a/ClockReceiver/VSyncPredictor.hpp b/ClockReceiver/VSyncPredictor.hpp
index 229a8d636..f34ed55c5 100644
--- a/ClockReceiver/VSyncPredictor.hpp
+++ b/ClockReceiver/VSyncPredictor.hpp
@@ -63,6 +63,13 @@ class VSyncPredictor {
 			frame_duration_ = Nanos(1'000'000'000.0f / rate);
 		}
 
+		/*!
+			@returns The time this class currently believes a whole frame occupies.
+		*/
+		Time::Nanos frame_duration() {
+			return frame_duration_;
+		}
+
 		/*!
 			Adds a record of how much jitter was experienced in scheduling; these values will be
 			factored into the @c suggested_draw_time if supplied.
@@ -87,15 +94,13 @@ class VSyncPredictor {
 			(if those figures are being supplied).
 		*/
 		Nanos suggested_draw_time() {
-			const auto mean = redraw_period_.mean() - timer_jitter_.mean() - vsync_jitter_.mean();
+			const auto mean = redraw_period_.mean() + timer_jitter_.mean() + vsync_jitter_.mean();
 			const auto variance = redraw_period_.variance() + timer_jitter_.variance() + vsync_jitter_.variance();
 
 			// Permit three standard deviations from the mean, to cover 99.9% of cases.
-			const auto period = mean - Nanos(3.0f * sqrt(float(variance)));
+			const auto period = mean + Nanos(3.0f * sqrt(float(variance)));
 
-			assert(abs(period) < 10'000'000'000);
-
-			return last_vsync_ + period;
+			return last_vsync_ + frame_duration_ - period;
 		}
 
 	private:
@@ -109,7 +114,6 @@ class VSyncPredictor {
 				}
 
 				void post(Time::Nanos value) {
-					assert(abs(value) < 10'000'000'000);	// 10 seconds is a very liberal maximum.
 					sum_ -= history_[write_pointer_];
 					sum_ += value;
 					history_[write_pointer_] = value;
diff --git a/OSBindings/Qt/scantargetwidget.cpp b/OSBindings/Qt/scantargetwidget.cpp
index 99072b486..3fbbc7c53 100644
--- a/OSBindings/Qt/scantargetwidget.cpp
+++ b/OSBindings/Qt/scantargetwidget.cpp
@@ -86,7 +86,7 @@ void ScanTargetWidget::vsync() {
 	const auto time_now = Time::nanos_now();
 	requestedRedrawTime = vsyncPredictor.suggested_draw_time();
 	const auto delay_time = (requestedRedrawTime - time_now) / 1'000'000;
-	if(delay_time > 0) {
+	if(delay_time > 0 && delay_time < vsyncPredictor.frame_duration()) {
 		QTimer::singleShot(delay_time, this, SLOT(repaint()));
 	} else {
 		requestedRedrawTime = 0;