diff --git a/layout/style/ServoStyleSheet.cpp b/layout/style/ServoStyleSheet.cpp
index 8b860c6bcd74..5e3b674953dc 100644
--- a/layout/style/ServoStyleSheet.cpp
+++ b/layout/style/ServoStyleSheet.cpp
@@ -18,13 +18,24 @@ using namespace mozilla::dom;
 
 namespace mozilla {
 
+// -------------------------------
+// CSS Style Sheet Inner Data Container
+//
+
+ServoStyleSheetInner::ServoStyleSheetInner(CORSMode aCORSMode,
+                                           ReferrerPolicy aReferrerPolicy,
+                                           const SRIMetadata& aIntegrity)
+  : StyleSheetInfo(aCORSMode, aReferrerPolicy, aIntegrity)
+{
+}
+
 ServoStyleSheet::ServoStyleSheet(css::SheetParsingMode aParsingMode,
                                  CORSMode aCORSMode,
                                  net::ReferrerPolicy aReferrerPolicy,
                                  const dom::SRIMetadata& aIntegrity)
   : StyleSheet(StyleBackendType::Servo, aParsingMode)
 {
-  mInner = new StyleSheetInfo(aCORSMode, aReferrerPolicy, aIntegrity);
+  mInner = new ServoStyleSheetInner(aCORSMode, aReferrerPolicy, aIntegrity);
   mInner->AddSheet(this);
 }
 
@@ -54,7 +65,7 @@ NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 bool
 ServoStyleSheet::HasRules() const
 {
-  return mSheet && Servo_StyleSheet_HasRules(mSheet);
+  return Inner()->mSheet && Servo_StyleSheet_HasRules(Inner()->mSheet);
 }
 
 nsresult
@@ -75,13 +86,13 @@ ServoStyleSheet::ParseSheet(css::Loader* aLoader,
   NS_ENSURE_SUCCESS(rv, rv);
 
   NS_ConvertUTF16toUTF8 input(aInput);
-  if (!mSheet) {
-    mSheet =
+  if (!Inner()->mSheet) {
+    Inner()->mSheet =
       Servo_StyleSheet_FromUTF8Bytes(aLoader, this, &input, mParsingMode,
                                      &baseString, base, referrer,
                                      principal).Consume();
   } else {
-    Servo_StyleSheet_ClearAndUpdate(mSheet, aLoader, this, &input, base,
+    Servo_StyleSheet_ClearAndUpdate(Inner()->mSheet, aLoader, this, &input, base,
                                     referrer, principal);
   }
 
@@ -91,7 +102,7 @@ ServoStyleSheet::ParseSheet(css::Loader* aLoader,
 void
 ServoStyleSheet::LoadFailed()
 {
-  mSheet = Servo_StyleSheet_Empty(mParsingMode).Consume();
+  Inner()->mSheet = Servo_StyleSheet_Empty(mParsingMode).Consume();
 }
 
 void
@@ -114,7 +125,8 @@ CSSRuleList*
 ServoStyleSheet::GetCssRulesInternal(ErrorResult& aRv)
 {
   if (!mRuleList) {
-    RefPtr<ServoCssRules> rawRules = Servo_StyleSheet_GetRules(mSheet).Consume();
+    RefPtr<ServoCssRules> rawRules =
+      Servo_StyleSheet_GetRules(Inner()->mSheet).Consume();
     mRuleList = new ServoCSSRuleList(this, rawRules.forget());
   }
   return mRuleList;
diff --git a/layout/style/ServoStyleSheet.h b/layout/style/ServoStyleSheet.h
index 6574049ca47b..5c28b727f69b 100644
--- a/layout/style/ServoStyleSheet.h
+++ b/layout/style/ServoStyleSheet.h
@@ -23,6 +23,20 @@ class Loader;
 class Rule;
 }
 
+// -------------------------------
+// Servo Style Sheet Inner Data Container
+//
+
+struct ServoStyleSheetInner : public StyleSheetInfo
+{
+  ServoStyleSheetInner(CORSMode aCORSMode,
+                       ReferrerPolicy aReferrerPolicy,
+                       const dom::SRIMetadata& aIntegrity);
+
+  RefPtr<RawServoStyleSheet> mSheet;
+};
+
+
 /**
  * CSS style sheet object that is a wrapper for a Servo Stylesheet.
  */
@@ -53,10 +67,12 @@ public:
    */
   void LoadFailed();
 
-  RawServoStyleSheet* RawSheet() const { return mSheet; }
+  RawServoStyleSheet* RawSheet() const {
+    return Inner()->mSheet;
+  }
   void SetSheetForImport(RawServoStyleSheet* aSheet) {
-    MOZ_ASSERT(!mSheet);
-    mSheet = aSheet;
+    MOZ_ASSERT(!Inner()->mSheet);
+    Inner()->mSheet = aSheet;
   }
 
   // WebIDL CSSStyleSheet API
@@ -73,6 +89,11 @@ public:
 protected:
   virtual ~ServoStyleSheet();
 
+  ServoStyleSheetInner* Inner() const
+  {
+    return static_cast<ServoStyleSheetInner*>(mInner);
+  }
+
   // Internal methods which do not have security check and completeness check.
   dom::CSSRuleList* GetCssRulesInternal(ErrorResult& aRv);
   uint32_t InsertRuleInternal(const nsAString& aRule,
@@ -84,7 +105,6 @@ protected:
 private:
   void DropRuleList();
 
-  RefPtr<RawServoStyleSheet> mSheet;
   RefPtr<ServoCSSRuleList> mRuleList;
 
   friend class StyleSheet;