diff --git a/layout/style/RuleCascadeData.cpp b/layout/style/RuleCascadeData.cpp
index 3a78e3e84e..7165a3967d 100644
--- a/layout/style/RuleCascadeData.cpp
+++ b/layout/style/RuleCascadeData.cpp
@@ -1622,7 +1622,9 @@ CascadeLayer::CascadeLayer(nsPresContext* aPresContext,
                            nsMediaQueryResultCacheKey& aCacheKey)
   : mPresContext(aPresContext)
   , mIsAnonymous(true)
+#ifdef DEBUG
   , mIsStrong(false)
+#endif
   , mRulesAdded(false)
 #ifdef DEBUG
   , mParent(aParent)
@@ -1655,7 +1657,9 @@ CascadeLayer::SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const
   // don't count them. Their ownership is managed by the rule processor
   // to which they are eventually attached (see nsCSSRuleProcessor).
   n += mPreLayers.ShallowSizeOfExcludingThis(aMallocSizeOf);
+#ifdef DEBUG
   n += mPostLayers.ShallowSizeOfExcludingThis(aMallocSizeOf);
+#endif
   n += mLayers.ShallowSizeOfExcludingThis(aMallocSizeOf);
   for (auto iter = mLayers.ConstIter(); !iter.Done(); iter.Next()) {
     // We don't own the CascadeLayer objects so we don't count them. We
@@ -1779,9 +1783,11 @@ CascadeLayer::EnumerateAllLayers(nsLayerEnumFunc aFunc, void* aData)
 
   (*aFunc)(this, aData);
 
+#ifdef DEBUG
   if (mPostLayers.Length() > 0) {
     for (CascadeLayer* post : mPostLayers) {
       post->EnumerateAllLayers(aFunc, aData);
     }
   }
+#endif
 }
diff --git a/layout/style/RuleCascadeData.h b/layout/style/RuleCascadeData.h
index 1a8b4efd07..bccb60d577 100644
--- a/layout/style/RuleCascadeData.h
+++ b/layout/style/RuleCascadeData.h
@@ -341,7 +341,9 @@ struct CascadeLayer
   nsPresContext* mPresContext;
   nsString mName;
   bool mIsAnonymous;
+#ifdef DEBUG
   bool mIsStrong;
+#endif
   bool mRulesAdded;
 
   RuleCascadeData* mData;
@@ -357,7 +359,9 @@ struct CascadeLayer
   CascadeLayer* mParent;
 #endif
   nsTArray<CascadeLayer*> mPreLayers;
+#ifdef DEBUG
   nsTArray<CascadeLayer*> mPostLayers;
+#endif
   nsDataHashtable<nsStringHashKey, CascadeLayer*> mLayers;
 
   CascadeLayer* CreateNamedChildLayer(const nsTArray<nsString>& aPath);