diff --git a/Cargo.lock b/Cargo.lock
index a18219b56837..4ce6029afe8a 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -4172,6 +4172,7 @@ dependencies = [
  "rustc_errors",
  "rustc_feature",
  "rustc_fluent_macro",
+ "rustc_index",
  "rustc_lexer",
  "rustc_macros",
  "rustc_session",
diff --git a/compiler/rustc_parse/Cargo.toml b/compiler/rustc_parse/Cargo.toml
index b33896154f23..c59ae48a07d0 100644
--- a/compiler/rustc_parse/Cargo.toml
+++ b/compiler/rustc_parse/Cargo.toml
@@ -12,6 +12,7 @@ rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_errors = { path = "../rustc_errors" }
 rustc_feature = { path = "../rustc_feature" }
 rustc_fluent_macro = { path = "../rustc_fluent_macro" }
+rustc_index = { path = "../rustc_index" }
 rustc_lexer = { path = "../rustc_lexer" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_session = { path = "../rustc_session" }
diff --git a/compiler/rustc_parse/src/parser/mod.rs b/compiler/rustc_parse/src/parser/mod.rs
index 39b5baada4c9..0b000916a55e 100644
--- a/compiler/rustc_parse/src/parser/mod.rs
+++ b/compiler/rustc_parse/src/parser/mod.rs
@@ -32,9 +32,10 @@ use rustc_ast::{
     VisibilityKind, DUMMY_NODE_ID,
 };
 use rustc_ast_pretty::pprust;
-use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::sync::Lrc;
 use rustc_errors::{Applicability, Diag, FatalError, MultiSpan, PResult};
+use rustc_index::interval::IntervalSet;
 use rustc_session::parse::ParseSess;
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::{Span, DUMMY_SP};
@@ -183,7 +184,7 @@ pub struct Parser<'a> {
 // This type is used a lot, e.g. it's cloned when matching many declarative macro rules with nonterminals. Make sure
 // it doesn't unintentionally get bigger.
 #[cfg(target_pointer_width = "64")]
-rustc_data_structures::static_assert_size!(Parser<'_>, 288);
+rustc_data_structures::static_assert_size!(Parser<'_>, 304);
 
 /// Stores span information about a closure.
 #[derive(Clone, Debug)]
@@ -261,7 +262,7 @@ struct CaptureState {
     capturing: Capturing,
     parser_replacements: Vec<ParserReplacement>,
     inner_attr_parser_ranges: FxHashMap<AttrId, ParserRange>,
-    seen_attrs: FxHashSet<AttrId>,
+    seen_attrs: IntervalSet<AttrId>,
 }
 
 /// Iterator over a `TokenStream` that produces `Token`s. It's a bit odd that
@@ -459,7 +460,7 @@ impl<'a> Parser<'a> {
                 capturing: Capturing::No,
                 parser_replacements: Vec::new(),
                 inner_attr_parser_ranges: Default::default(),
-                seen_attrs: Default::default(),
+                seen_attrs: IntervalSet::new(u32::MAX as usize),
             },
             current_closure: None,
             recovery: Recovery::Allowed,