--- a/gfx/layers/apz/src/AsyncPanZoomController.cpp
+++ b/gfx/layers/apz/src/AsyncPanZoomController.cpp
@@ -1500,16 +1500,17 @@ AsyncPanZoomController::AllowScrollHando
 {
   WheelBlockState* block = mInputQueue->CurrentWheelBlock();
   return block->AllowScrollHandoff();
 }
 
 nsEventStatus AsyncPanZoomController::OnScrollWheel(const ScrollWheelInput& aEvent)
 {
   LayoutDevicePoint delta = GetScrollWheelDelta(aEvent);
+  APZC_LOG("%p got a scroll-wheel with delta %s\n", this, Stringify(delta).c_str());
 
   if ((delta.x || delta.y) &&
       !CanScrollWithWheel(delta) &&
       mInputQueue->GetCurrentWheelTransaction())
   {
     // We can't scroll this apz anymore, so we simply drop the event.
     if (gfxPrefs::MouseScrollTestingEnabled()) {
       if (nsRefPtr<GeckoContentController> controller = GetGeckoContentController()) {

--- a/gfx/tests/gtest/TestAsyncPanZoomController.cpp
+++ b/gfx/tests/gtest/TestAsyncPanZoomController.cpp
@@ -1894,16 +1894,18 @@ protected:
                                         CSSRect aScrollableRect = CSSRect(-1, -1, -1, -1)) {
     FrameMetrics metrics;
     metrics.SetScrollId(aScrollId);
     IntRect layerBound = aLayer->GetVisibleRegion().GetBounds();
     metrics.SetCompositionBounds(ParentLayerRect(layerBound.x, layerBound.y,
                                                  layerBound.width, layerBound.height));
     metrics.SetScrollableRect(aScrollableRect);
     metrics.SetScrollOffset(CSSPoint(0, 0));
+    metrics.SetPageScrollAmount(LayoutDeviceIntSize(50, 100));
+    metrics.SetAllowVerticalScrollWithWheel();
     aLayer->SetFrameMetrics(metrics);
     aLayer->SetClipRect(Some(ViewAs<ParentLayerPixel>(layerBound)));
     if (!aScrollableRect.IsEqualEdges(CSSRect(-1, -1, -1, -1))) {
       // The purpose of this is to roughly mimic what layout would do in the
       // case of a scrollable frame with the event regions and clip. This lets
       // us exercise the hit-testing code in APZCTreeManager
       EventRegions er = aLayer->GetEventRegions();
       IntRect scrollRect = LayerIntRect::ToUntyped(RoundedToInt(aScrollableRect * metrics.LayersPixelsPerCSSPixel()));
@@ -2419,16 +2421,47 @@ TEST_F(APZHitTestingTester, TestRepaintF
 
   mti.mType = MultiTouchInput::MULTITOUCH_END;
   EXPECT_EQ(nsEventStatus_eConsumeDoDefault, manager->ReceiveInputEvent(mti, nullptr, nullptr));
   EXPECT_EQ(touchPoint, mti.mTouches[0].mScreenPoint);
 
   mcc->RunThroughDelayedTasks();
 }
 
+TEST_F(APZHitTestingTester, TestRepaintFlushOnWheelEvents) {
+  // The purpose of this test is to ensure that wheel events trigger a repaint
+  // flush as per bug 1166871, and that the wheel event untransform is a no-op.
+
+  CreateSimpleScrollingLayer();
+  ScopedLayerTreeRegistration registration(0, root, mcc);
+  manager->UpdateHitTestingTree(nullptr, root, false, 0, 0);
+  TestAsyncPanZoomController* apzcroot = ApzcOf(root);
+
+  EXPECT_CALL(*mcc, RequestContentRepaint(_)).Times(AtLeast(3));
+  ScreenPoint origin(100, 50);
+  for (int i = 0; i < 3; i++) {
+    ScrollWheelInput swi(MillisecondsSinceStartup(mTime), mTime, 0,
+      ScrollWheelInput::SCROLLMODE_INSTANT, ScrollWheelInput::SCROLLDELTA_PIXEL,
+      origin, 0, 10);
+    EXPECT_EQ(nsEventStatus_eConsumeDoDefault, manager->ReceiveInputEvent(swi, nullptr, nullptr));
+    EXPECT_EQ(origin, swi.mOrigin);
+
+    ViewTransform viewTransform;
+    ParentLayerPoint point;
+    apzcroot->SampleContentTransformForFrame(mTime, &viewTransform, point);
+    EXPECT_EQ(0, point.x);
+    EXPECT_EQ((i + 1) * 10, point.y);
+    EXPECT_EQ(0, viewTransform.mTranslation.x);
+    EXPECT_EQ((i + 1) * -10, viewTransform.mTranslation.y);
+
+    mTime += TimeDuration::FromMilliseconds(5);
+  }
+  mcc->RunThroughDelayedTasks();
+}
+
 TEST_F(APZHitTestingTester, Bug1148350) {
   CreateBug1148350LayerTree();
   ScopedLayerTreeRegistration registration(0, root, mcc);
   manager->UpdateHitTestingTree(nullptr, root, false, 0, 0);
 
   MockFunction<void(std::string checkPointName)> check;
   {
     InSequence s;