diff --git a/Rendering/RayTracing/vtkOSPRayRendererNode.cxx b/Rendering/RayTracing/vtkOSPRayRendererNode.cxx
index ac028dad1ed5ebf0c8d53d6593dda72385dbe673..46d157d22105d21434b1259b7eeb75b06ba63bd9 100644
--- a/Rendering/RayTracing/vtkOSPRayRendererNode.cxx
+++ b/Rendering/RayTracing/vtkOSPRayRendererNode.cxx
@@ -1511,7 +1511,8 @@ void vtkOSPRayRendererNode::Render(bool prepass)
           static_cast<unsigned char>(std::min(this->ColorBuffer[i].y * 255.f, 255.f));
         this->Buffer[bi + 2] =
           static_cast<unsigned char>(std::min(this->ColorBuffer[i].z * 255.f, 255.f));
-        this->Buffer[bi + 3] = 255;
+        this->Buffer[bi + 3] =
+          static_cast<unsigned char>(std::min(this->ColorBuffer[i].w * 255.f, 255.f));
       }
 #else
       // std::copy((unsigned char*)rgba, this->Size[0]*this->Size[1]*4*sizeof(float),