--- a/layout/style/nsCSSCounterStyleRule.cpp
+++ b/layout/style/nsCSSCounterStyleRule.cpp
@@ -407,30 +407,43 @@ nsCSSCounterStyleRule::CheckDescValue(in
       return true;
   }
 }
 
 nsresult
 nsCSSCounterStyleRule::SetDescriptor(nsCSSCounterDesc aDescID,
                                      const nsAString& aValue)
 {
-  nsCSSParser parser;
   nsCSSValue value;
-  nsIURI* baseURL = nullptr;
-  nsIPrincipal* principal = nullptr;
-  if (StyleSheet* sheet = GetStyleSheet()) {
-    baseURL = sheet->GetBaseURI();
-    principal = sheet->Principal();
+  bool ok;
+
+  StyleSheet* sheet = GetStyleSheet();
+
+#ifdef MOZ_STYLO
+  bool useServo = !sheet || sheet->IsServo();
+#else
+  bool useServo = false;
+#endif
+
+  if (useServo) {
+    URLExtraData* data = sheet ? sheet->AsServo()->URLData() : nullptr;
+    ok = ServoCSSParser::ParseCounterStyleDescriptor(aDescID, aValue, data,
+                                                     value);
+  } else {
+    nsCSSParser parser;
+    nsIURI* baseURL = sheet ? sheet->GetBaseURI() : nullptr;
+    nsIPrincipal* principal = sheet ? sheet->Principal() : nullptr;
+    ok = parser.ParseCounterDescriptor(aDescID, aValue, nullptr,
+                                       baseURL, principal, value);
   }
-  if (parser.ParseCounterDescriptor(aDescID, aValue, nullptr,
-                                    baseURL, principal, value)) {
-    if (CheckDescValue(GetSystem(), aDescID, value)) {
-      SetDesc(aDescID, value);
-    }
+
+  if (ok && CheckDescValue(GetSystem(), aDescID, value)) {
+    SetDesc(aDescID, value);
   }
+
   return NS_OK;
 }
 
 #define CSS_COUNTER_DESC_SETTER(name_)                        \
 NS_IMETHODIMP                                                 \
 nsCSSCounterStyleRule::Set##name_(const nsAString& a##name_)  \
 {                                                             \
   return SetDescriptor(eCSSCounterDesc_##name_, a##name_);    \