diff --git a/src/pbrt/gpu/denoiser.cpp b/src/pbrt/gpu/denoiser.cpp
index db66c5f346576eae889882856badd5b62f5d6f43..ccb6783f947be0fd95755b0ae855c217c8204861 100644
--- a/src/pbrt/gpu/denoiser.cpp
+++ b/src/pbrt/gpu/denoiser.cpp
@@ -101,7 +101,7 @@ void Denoiser::Denoise(RGB *rgb, Normal3f *n, RGB *albedo, RGB *result) {
         CUdeviceptr(scratchBuffer), memorySizes.withoutOverlapScratchSizeInBytes));
 
     OptixDenoiserParams params = {};
-    params.denoiseAlpha = 0;
+    params.denoiseAlpha = OPTIX_DENOISER_ALPHA_MODE_COPY;
     params.hdrIntensity = CUdeviceptr(intensity);
     params.blendFactor = 0;  // TODO what should this be??