--- a/dom/canvas/WebGLContext.cpp
+++ b/dom/canvas/WebGLContext.cpp
@@ -1980,17 +1980,16 @@ WebGLContext::GetSurfaceSnapshot(gfxAlph
     }
 
     if (out_alphaType) {
         *out_alphaType = alphaType;
     } else {
         // Expects Opaque or Premult
         if (alphaType == gfxAlphaType::NonPremult) {
             gfxUtils::PremultiplyDataSurface(surf, surf);
-            alphaType = gfxAlphaType::Premult;
         }
     }
 
     RefPtr<DrawTarget> dt =
         Factory::CreateDrawTarget(gfxPlatform::GetPlatform()->GetSoftwareBackend(),
                                   IntSize(mWidth, mHeight),
                                   SurfaceFormat::B8G8R8A8);
     if (!dt)