diff --git a/validator/cpp/engine/validator-internal.cc b/validator/cpp/engine/validator-internal.cc
index 21058500c2844..63856a5eb540d 100644
--- a/validator/cpp/engine/validator-internal.cc
+++ b/validator/cpp/engine/validator-internal.cc
@@ -644,9 +644,9 @@ struct ParsedReferencePoint {
 class ParsedReferencePoints {
  public:
   ParsedReferencePoints() : parent_(nullptr) {}
-  ParsedReferencePoints(
-      const TagSpec& parent,
-      const unordered_map<std::string, int32_t>& tag_spec_ids_by_tag_spec_name)
+  ParsedReferencePoints(const TagSpec& parent,
+                        const absl::flat_hash_map<std::string, int32_t>&
+                            tag_spec_ids_by_tag_spec_name)
       : parent_(&parent) {
     for (const ReferencePoint& p : parent.reference_points()) {
       auto iter = tag_spec_ids_by_tag_spec_name.find(p.tag_spec_name());
@@ -1041,11 +1041,11 @@ RecordValidated ShouldRecordTagspecValidated(
 // which is unique within its context, the ParsedValidatorRules.
 class ParsedTagSpec {
  public:
-  ParsedTagSpec(
-      ParsedAttrSpecs* parsed_attr_specs,
-      const unordered_map<std::string, int32_t>& tag_spec_ids_by_tag_spec_name,
-      RecordValidated should_record_tagspec_validated, const TagSpec* spec,
-      int32_t id)
+  ParsedTagSpec(ParsedAttrSpecs* parsed_attr_specs,
+                const absl::flat_hash_map<std::string, int32_t>&
+                    tag_spec_ids_by_tag_spec_name,
+                RecordValidated should_record_tagspec_validated,
+                const TagSpec* spec, int32_t id)
       : spec_(spec),
         id_(id),
         reference_points_(*spec, tag_spec_ids_by_tag_spec_name),
@@ -1218,7 +1218,7 @@ class ParsedTagSpec {
 
   const set<int32_t>& implicit_attrspecs() const { return implicit_attrspecs_; }
 
-  const unordered_map<std::string, int32_t>& attr_ids_by_name() const {
+  const absl::flat_hash_map<std::string, int32_t>& attr_ids_by_name() const {
     return attr_ids_by_name_;
   }
 
@@ -1240,7 +1240,7 @@ class ParsedTagSpec {
   bool is_reference_point_;
   bool is_type_json_ = false;
   bool contains_url_ = false;
-  unordered_map<std::string, int32_t> attr_ids_by_name_;
+  absl::flat_hash_map<std::string, int32_t> attr_ids_by_name_;
   vector<TypeIdentifier> disabled_by_;
   vector<TypeIdentifier> enabled_by_;
   vector<int32_t> mandatory_attr_ids_;
@@ -2476,7 +2476,7 @@ class Context {
     if (!tag_result.best_match_tag_spec) return;
     const ParsedTagSpec* parsed_tag_spec = tag_result.best_match_tag_spec;
     if (!parsed_tag_spec->AttrsCanSatisfyExtension()) return;
-    const unordered_map<std::string, int32_t>& attr_ids_by_name =
+    const absl::flat_hash_map<std::string, int32_t>& attr_ids_by_name =
         parsed_tag_spec->attr_ids_by_name();
     ExtensionsContext* extensions_ctx = mutable_extensions();
     for (const ParsedHtmlTagAttr& attr : encountered_tag.Attributes()) {
@@ -4412,7 +4412,7 @@ void ValidateAttributes(const ParsedTagSpec& parsed_tag_spec,
   set<std::string_view> mandatory_anyofs_seen;
   vector<const ParsedAttrTriggerSpec*> parsed_trigger_specs;
   set<int32_t> attrspecs_validated;
-  const unordered_map<std::string, int32_t>& attr_ids_by_name =
+  const absl::flat_hash_map<std::string, int32_t>& attr_ids_by_name =
       parsed_tag_spec.attr_ids_by_name();
 
   for (const ParsedHtmlTagAttr& attr : encountered_tag.Attributes()) {
@@ -4717,7 +4717,7 @@ ParsedValidatorRules::ParsedValidatorRules(HtmlFormat::Code html_format)
   // |tag_spec_names_to_track| to identify those tagspecs that are
   // referenced by others via "also_requires_tag".  The ParsedTagSpec
   // constructor completes this translation to ids.
-  unordered_map<std::string, int32_t> tag_spec_ids_by_tag_spec_name;
+  absl::flat_hash_map<std::string, int32_t> tag_spec_ids_by_tag_spec_name;
   unordered_set<std::string> tag_spec_names_to_track;
   for (int ii = 0; ii < rules_.tags_size(); ++ii) {
     const TagSpec& tag = rules_.tags(ii);