--- a/layout/style/CounterStyleManager.cpp
+++ b/layout/style/CounterStyleManager.cpp
@@ -2003,33 +2003,26 @@ CounterStyleManager::Disconnect()
   }
   mStyles.Clear();
   mPresContext = nullptr;
 }
 
 CounterStyle*
 CounterStyleManager::BuildCounterStyle(nsIAtom* aName)
 {
+  MOZ_ASSERT(NS_IsMainThread());
   CounterStyle* data = mStyles.Get(aName);
   if (data) {
     return data;
   }
 
   // It is intentional that the predefined names are case-insensitive
   // but the user-defined names case-sensitive.
-  // XXXheycam ServoStyleSets do not support custom counter styles yet.  Bug
-  // 1328319.
   StyleSetHandle styleSet = mPresContext->StyleSet();
-  // When this assertion is removed, please remove the hack to avoid it in
-  // nsStyleList::nsStyleList.
-  NS_ASSERTION(styleSet->IsGecko(),
-               "stylo: ServoStyleSets do not support custom counter "
-               "styles yet");
-  nsCSSCounterStyleRule* rule = styleSet->IsGecko() ?
-    styleSet->AsGecko()->CounterStyleRuleForName(aName) : nullptr;
+  nsCSSCounterStyleRule* rule = styleSet->CounterStyleRuleForName(aName);
   if (rule) {
     MOZ_ASSERT(rule->Name() == aName);
     data = new (mPresContext) CustomCounterStyle(aName, this, rule);
   } else {
     int32_t type;
     nsDependentAtomString name(aName);
     nsCSSKeyword keyword = nsCSSKeywords::LookupKeyword(name);
     if (nsCSSProps::FindKeyword(keyword, nsCSSProps::kListStyleKTable, type)) {
@@ -2060,26 +2053,18 @@ CounterStyleManager::GetBuiltinStyle(int
 bool
 CounterStyleManager::NotifyRuleChanged()
 {
   bool changed = false;
   for (auto iter = mStyles.Iter(); !iter.Done(); iter.Next()) {
     CounterStyle* style = iter.Data();
     bool toBeUpdated = false;
     bool toBeRemoved = false;
-    // XXXheycam ServoStyleSets do not support custom counter styles yet.  Bug
-    // 1328319.
     StyleSetHandle styleSet = mPresContext->StyleSet();
-    // When this assertion is removed, please remove the hack to avoid it in
-    // nsStyleList::nsStyleList.
-    NS_ASSERTION(styleSet->IsGecko(),
-                 "stylo: ServoStyleSets do not support custom counter "
-                 "styles yet");
-    nsCSSCounterStyleRule* newRule = styleSet->IsGecko() ?
-        styleSet->AsGecko()->CounterStyleRuleForName(iter.Key()) : nullptr;
+    nsCSSCounterStyleRule* newRule = styleSet->CounterStyleRuleForName(iter.Key());
     if (!newRule) {
       if (style->IsCustomStyle()) {
         toBeRemoved = true;
       }
     } else {
       if (!style->IsCustomStyle()) {
         toBeRemoved = true;
       } else {

--- a/layout/style/ServoBindingList.h
+++ b/layout/style/ServoBindingList.h
@@ -74,16 +74,18 @@ SERVO_BINDING_FUNC(Servo_StyleSet_GetKey
                    RawServoStyleSetBorrowed set,
                    const nsACString* property,
                    nsTimingFunctionBorrowed timing_function,
                    ServoComputedValuesBorrowed computed_values,
                    RawGeckoKeyframeListBorrowedMut keyframe_list)
 SERVO_BINDING_FUNC(Servo_StyleSet_GetFontFaceRules, void,
                    RawServoStyleSetBorrowed set,
                    RawGeckoFontFaceRuleListBorrowedMut list)
+SERVO_BINDING_FUNC(Servo_StyleSet_GetCounterStyleRule, nsCSSCounterStyleRule*,
+                   RawServoStyleSetBorrowed set, nsIAtom* name)
 SERVO_BINDING_FUNC(Servo_StyleSet_ResolveForDeclarations,
                    ServoComputedValuesStrong,
                    RawServoStyleSetBorrowed set,
                    ServoComputedValuesBorrowedOrNull parent_style,
                    RawServoDeclarationBlockBorrowed declarations)
 
 // CSSRuleList
 SERVO_BINDING_FUNC(Servo_CssRules_ListTypes, void,

--- a/layout/style/ServoStyleSet.cpp
+++ b/layout/style/ServoStyleSet.cpp
@@ -1038,16 +1038,22 @@ ServoStyleSet::ResolveStyleLazily(Elemen
 bool
 ServoStyleSet::AppendFontFaceRules(nsTArray<nsFontFaceRuleContainer>& aArray)
 {
   MaybeRebuildStylist();
   Servo_StyleSet_GetFontFaceRules(mRawSet.get(), &aArray);
   return true;
 }
 
+nsCSSCounterStyleRule*
+ServoStyleSet::CounterStyleRuleForName(nsIAtom* aName)
+{
+  return Servo_StyleSet_GetCounterStyleRule(mRawSet.get(), aName);
+}
+
 already_AddRefed<ServoComputedValues>
 ServoStyleSet::ResolveForDeclarations(
   ServoComputedValuesBorrowedOrNull aParentOrNull,
   RawServoDeclarationBlockBorrowed aDeclarations)
 {
   MaybeRebuildStylist();
   return Servo_StyleSet_ResolveForDeclarations(mRawSet.get(),
                                                aParentOrNull,

--- a/layout/style/ServoStyleSet.h
+++ b/layout/style/ServoStyleSet.h
@@ -29,16 +29,17 @@ class Element;
 } // namespace dom
 class CSSStyleSheet;
 class ServoRestyleManager;
 class ServoStyleSheet;
 struct Keyframe;
 struct ServoComputedValuesWithParent;
 class ServoElementSnapshotTable;
 } // namespace mozilla
+class nsCSSCounterStyleRule;
 class nsIContent;
 class nsIDocument;
 class nsStyleContext;
 class nsPresContext;
 struct nsTimingFunction;
 struct RawServoRuleNode;
 struct TreeMatchContext;
 
@@ -305,16 +306,18 @@ public:
   nsTArray<ComputedKeyframeValues>
   GetComputedKeyframeValuesFor(const nsTArray<Keyframe>& aKeyframes,
                                dom::Element* aElement,
                                const ServoComputedValuesWithParent&
                                  aServoValues);
 
   bool AppendFontFaceRules(nsTArray<nsFontFaceRuleContainer>& aArray);
 
+  nsCSSCounterStyleRule* CounterStyleRuleForName(nsIAtom* aName);
+
   already_AddRefed<ServoComputedValues>
   GetBaseComputedValuesForElement(dom::Element* aElement, nsIAtom* aPseudoTag);
 
   /**
    * Resolve style for a given declaration block with/without the parent style.
    * If the parent style is not specified, the document default computed values
    * is used.
    */

--- a/layout/style/StyleSetHandle.h
+++ b/layout/style/StyleSetHandle.h
@@ -19,16 +19,17 @@
 
 namespace mozilla {
 class CSSStyleSheet;
 class ServoStyleSet;
 namespace dom {
 class Element;
 } // namespace dom
 } // namespace mozilla
+class nsCSSCounterStyleRule;
 struct nsFontFaceRuleContainer;
 class nsIAtom;
 class nsIContent;
 class nsIDocument;
 class nsStyleContext;
 class nsStyleSet;
 class nsPresContext;
 struct TreeMatchContext;
@@ -169,16 +170,17 @@ public:
         mozilla::CSSPseudoElementType aPseudoType,
         dom::Element* aPseudoElement,
         EventStates aStateMask);
 
     inline void RootStyleContextAdded();
     inline void RootStyleContextRemoved();
 
     inline bool AppendFontFaceRules(nsTArray<nsFontFaceRuleContainer>& aArray);
+    inline nsCSSCounterStyleRule* CounterStyleRuleForName(nsIAtom* aName);
 
   private:
     // Stores a pointer to an nsStyleSet or a ServoStyleSet.  The least
     // significant bit is 0 for the former, 1 for the latter.  This is
     // valid as the least significant bit will never be used for a pointer
     // value on platforms we care about.
     uintptr_t mValue;
   };

--- a/layout/style/StyleSetHandleInlines.h
+++ b/layout/style/StyleSetHandleInlines.h
@@ -274,13 +274,19 @@ StyleSetHandle::Ptr::RootStyleContextRem
 
 bool
 StyleSetHandle::Ptr::
 AppendFontFaceRules(nsTArray<nsFontFaceRuleContainer>& aArray)
 {
   FORWARD(AppendFontFaceRules, (aArray));
 }
 
+nsCSSCounterStyleRule*
+StyleSetHandle::Ptr::CounterStyleRuleForName(nsIAtom* aName)
+{
+  FORWARD(CounterStyleRuleForName, (aName));
+}
+
 } // namespace mozilla
 
 #undef FORWARD
 
 #endif // mozilla_StyleSetHandleInlines_h