diff --git a/compiler/rustc_data_structures/src/sync/vec.rs b/compiler/rustc_data_structures/src/sync/vec.rs
index 99de33685f6..64b0aff6ca2 100644
--- a/compiler/rustc_data_structures/src/sync/vec.rs
+++ b/compiler/rustc_data_structures/src/sync/vec.rs
@@ -76,3 +76,19 @@ impl<T: Copy> AppendOnlyVec<T> {
         return self.vec.get(i);
     }
 }
+
+impl<T: Copy + PartialEq> AppendOnlyVec<T> {
+    pub fn contains(&self, val: T) -> bool {
+        for i in 0.. {
+            match self.get(i) {
+                None => return false,
+                Some(v) => {
+                    if val == v {
+                        return true;
+                    }
+                }
+            }
+        }
+        false
+    }
+}
diff --git a/compiler/rustc_lint/src/builtin.rs b/compiler/rustc_lint/src/builtin.rs
index c1b247e3d61..6b387df785e 100644
--- a/compiler/rustc_lint/src/builtin.rs
+++ b/compiler/rustc_lint/src/builtin.rs
@@ -1947,7 +1947,7 @@ impl KeywordIdents {
         };
 
         // Don't lint `r#foo`.
-        if cx.sess().parse_sess.raw_identifier_spans.borrow().contains(&ident.span) {
+        if cx.sess().parse_sess.raw_identifier_spans.contains(ident.span) {
             return;
         }
 
diff --git a/compiler/rustc_parse/src/lexer/mod.rs b/compiler/rustc_parse/src/lexer/mod.rs
index 9dbddee5a56..4a7da11a097 100644
--- a/compiler/rustc_parse/src/lexer/mod.rs
+++ b/compiler/rustc_parse/src/lexer/mod.rs
@@ -175,7 +175,7 @@ impl<'a> StringReader<'a> {
                     if !sym.can_be_raw() {
                         self.sess.emit_err(errors::CannotBeRawIdent { span, ident: sym });
                     }
-                    self.sess.raw_identifier_spans.borrow_mut().push(span);
+                    self.sess.raw_identifier_spans.push(span);
                     token::Ident(sym, true)
                 }
                 rustc_lexer::TokenKind::UnknownPrefix => {
diff --git a/compiler/rustc_session/src/parse.rs b/compiler/rustc_session/src/parse.rs
index d80911747f3..61ce9291040 100644
--- a/compiler/rustc_session/src/parse.rs
+++ b/compiler/rustc_session/src/parse.rs
@@ -194,7 +194,7 @@ pub struct ParseSess {
     pub edition: Edition,
     /// Places where raw identifiers were used. This is used to avoid complaining about idents
     /// clashing with keywords in new editions.
-    pub raw_identifier_spans: Lock<Vec<Span>>,
+    pub raw_identifier_spans: AppendOnlyVec<Span>,
     /// Places where identifiers that contain invalid Unicode codepoints but that look like they
     /// should be. Useful to avoid bad tokenization when encountering emoji. We group them to
     /// provide a single error per unique incorrect identifier.
@@ -247,7 +247,7 @@ impl ParseSess {
             config: FxIndexSet::default(),
             check_config: CrateCheckConfig::default(),
             edition: ExpnId::root().expn_data().edition,
-            raw_identifier_spans: Lock::new(Vec::new()),
+            raw_identifier_spans: Default::default(),
             bad_unicode_identifiers: Lock::new(Default::default()),
             source_map,
             buffered_lints: Lock::new(vec![]),