diff --git a/layout/base/FrameLayerBuilder.cpp b/layout/base/FrameLayerBuilder.cpp
index 39484d977dd..dc7666f743f 100644
--- a/layout/base/FrameLayerBuilder.cpp
+++ b/layout/base/FrameLayerBuilder.cpp
@@ -1608,9 +1608,9 @@ AppUnitsPerDevPixel(nsDisplayItem* aItem)
  * Because we only reduce the visible region here, we don't need to worry
  * about whether CONTENT_OPAQUE is set; if layer was opaque in the old
  * visible region, it will still be opaque in the new one.
- * @param aLayerVisibleRegion the visible region of the layer, in the layer's
- * coordinate space
- * @param aRestrictToRect the rect to restrict the visible region to, in the
+ * @param aLayerVisibleRect if non-null, the visible rect of the layer, in
+ * the layer's coordinate space
+ * @param aOuterVisibleRect the rect to restrict the visible region to, in the
  * parent's coordinate system
  */
 static void
diff --git a/layout/base/nsLayoutUtils.cpp b/layout/base/nsLayoutUtils.cpp
index 8bb035fad98..08c5edc14ff 100644
--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -1483,7 +1483,7 @@ nsLayoutUtils::GetScrollableFrameFor(const nsIFrame *aScrolledFrame)
 {
   nsIFrame *frame = aScrolledFrame->GetParent();
   nsIScrollableFrame *sf = do_QueryFrame(frame);
-  return sf;
+  return sf && sf->GetScrolledFrame() == aScrolledFrame ? sf : nullptr;
 }
 
 /* static */ void