2 files changed, 3 insertions, 1 deletions
diff --git a/Source/WebCore/rendering/RenderLayer.cpp b/Source/WebCore/rendering/RenderLayer.cpp
index c378f18e6..2d0b56e79 100644
--- a/Source/WebCore/rendering/RenderLayer.cpp
+++ b/Source/WebCore/rendering/RenderLayer.cpp
@@ -3619,6 +3619,7 @@ void RenderLayer::paintLayer(GraphicsContext* context, const LayerPaintingInfo&
     } else if (viewportConstrainedNotCompositedReason() == NotCompositedForBoundsOutOfView) {
         // Don't paint out-of-view viewport constrained layers (when doing prepainting) because they will never be visible
         // unless their position or viewport size is changed.
+        ASSERT(renderer()->style()->position() == FixedPosition);
         return;
     }
 #endif
diff --git a/Source/WebCore/rendering/RenderLayerCompositor.cpp b/Source/WebCore/rendering/RenderLayerCompositor.cpp
index 6f1fd3e0b..784ebdc80 100644
--- a/Source/WebCore/rendering/RenderLayerCompositor.cpp
+++ b/Source/WebCore/rendering/RenderLayerCompositor.cpp
@@ -767,7 +767,8 @@ bool RenderLayerCompositor::updateBacking(RenderLayer* layer, CompositingChangeR
             if (ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator())
                 scrollingCoordinator->frameViewFixedObjectsDidChange(m_renderView->frameView());
         }
-    }
+    } else
+        layer->setViewportConstrainedNotCompositedReason(RenderLayer::NoNotCompositedReason);
     
     if (layer->backing())
         layer->backing()->updateDebugIndicators(m_showDebugBorders, m_showRepaintCounter);