--- a/widget/nsBaseWidget.cpp
+++ b/widget/nsBaseWidget.cpp
@@ -1360,17 +1360,17 @@ already_AddRefed<mozilla::gfx::DrawTarge
   return nullptr;
 }
 
 already_AddRefed<mozilla::gfx::DrawTarget>
 nsBaseWidget::CreateBackBufferDrawTarget(mozilla::gfx::DrawTarget* aScreenTarget,
                                          const LayoutDeviceIntRect& aRect)
 {
   MOZ_ASSERT(aScreenTarget);
-  gfx::SurfaceFormat format = aScreenTarget->GetFormat() == gfx::SurfaceFormat::B8G8R8X8 ? gfx::SurfaceFormat::B8G8R8X8 : gfx::SurfaceFormat::B8G8R8A8;
+  gfx::SurfaceFormat format = gfx::SurfaceFormat::B8G8R8A8;
   return aScreenTarget->CreateSimilarDrawTarget(aRect.ToUnknownRect().Size(), format);
 }
 
 //-------------------------------------------------------------------------
 //
 // Destroy the window
 //
 //-------------------------------------------------------------------------