--- a/gfx/layers/composite/AsyncCompositionManager.cpp
+++ b/gfx/layers/composite/AsyncCompositionManager.cpp
@@ -1101,16 +1101,17 @@ ApplyAsyncTransformToScrollbarForContent
   // layer has been built for a scroll frame, as this would result in a
   // disparity between scrollbars and visible content.
   if (aContent.IsScrollInfoLayer()) {
     return;
   }
 
   const FrameMetrics& metrics = aContent.Metrics();
   AsyncPanZoomController* apzc = aContent.GetApzc();
+  MOZ_RELEASE_ASSERT(apzc);
 
   AsyncTransformComponentMatrix asyncTransform =
     apzc->GetCurrentAsyncTransform(AsyncPanZoomController::RESPECT_FORCE_DISABLE);
 
   // |asyncTransform| represents the amount by which we have scrolled and
   // zoomed since the last paint. Because the scrollbar was sized and positioned based
   // on the painted content, we need to adjust it based on asyncTransform so that
   // it reflects what the user is actually seeing now.