diff --git a/layout/painting/nsDisplayList.cpp b/layout/painting/nsDisplayList.cpp
index 6e9950b97432..48efc80f72bf 100644
--- a/layout/painting/nsDisplayList.cpp
+++ b/layout/painting/nsDisplayList.cpp
@@ -7353,6 +7353,8 @@ bool nsDisplayMask::ShouldPaintOnMaskLayer(LayerManager* aManager)
   nsSVGUtils::MaskUsage maskUsage;
   nsSVGUtils::DetermineMaskUsage(mFrame, mHandleOpacity, maskUsage);
 
+  // XXX Bug 1323912. nsSVGIntegrationUtils::PaintMask can not handle opacity
+  // correctly. Turn it off before bug fixed.
   if (maskUsage.opacity != 1.0) {
     return false;
   }
diff --git a/layout/svg/nsSVGIntegrationUtils.cpp b/layout/svg/nsSVGIntegrationUtils.cpp
index 7743e9b9c98d..07d37e3cdcf8 100644
--- a/layout/svg/nsSVGIntegrationUtils.cpp
+++ b/layout/svg/nsSVGIntegrationUtils.cpp
@@ -804,9 +804,10 @@ nsSVGIntegrationUtils::PaintMask(const PaintFramesParams& aParams)
     SetupContextMatrix(frame, aParams, offsetToBoundingBox,
                        offsetToUserSpace);
     nsTArray<nsSVGMaskFrame *> maskFrames = effectProperties.GetMaskFrames();
-    bool opacityApplied = !HasNonSVGMask(maskFrames);
-    result = PaintMaskSurface(aParams, maskTarget,
-                              opacityApplied ? maskUsage.opacity : 1.0,
+    // XXX Bug 1323912.
+    MOZ_ASSERT(maskUsage.opacity == 1.0,
+               "nsSVGIntegrationUtils::PaintMask can not handle opacity now.");
+    result = PaintMaskSurface(aParams, maskTarget, 1.0,
                               firstFrame->StyleContext(), maskFrames,
                               ctx.CurrentMatrix(), offsetToUserSpace);
     if (result != DrawResult::SUCCESS) {