diff --git a/compiler/rustc_data_structures/src/sync/vec.rs b/compiler/rustc_data_structures/src/sync/vec.rs
index 6ffd2a75e81..99de33685f6 100644
--- a/compiler/rustc_data_structures/src/sync/vec.rs
+++ b/compiler/rustc_data_structures/src/sync/vec.rs
@@ -2,6 +2,7 @@ use std::marker::PhantomData;
 
 use rustc_index::vec::Idx;
 
+#[derive(Default)]
 pub struct AppendOnlyIndexVec<I: Idx, T: Copy> {
     #[cfg(not(parallel_compiler))]
     vec: elsa::vec::FrozenVec<T>,
@@ -40,6 +41,7 @@ impl<I: Idx, T: Copy> AppendOnlyIndexVec<I, T> {
     }
 }
 
+#[derive(Default)]
 pub struct AppendOnlyVec<T: Copy> {
     #[cfg(not(parallel_compiler))]
     vec: elsa::vec::FrozenVec<T>,
@@ -57,11 +59,14 @@ impl<T: Copy> AppendOnlyVec<T> {
         }
     }
 
-    pub fn push(&self, val: T) {
+    pub fn push(&self, val: T) -> usize {
+        #[cfg(not(parallel_compiler))]
+        let i = self.vec.len();
         #[cfg(not(parallel_compiler))]
         self.vec.push(val);
         #[cfg(parallel_compiler)]
-        self.vec.push(val)
+        let i = self.vec.push(val);
+        i
     }
 
     pub fn get(&self, i: usize) -> Option<T> {
diff --git a/compiler/rustc_metadata/src/rmeta/encoder.rs b/compiler/rustc_metadata/src/rmeta/encoder.rs
index 2652a4280d3..0e8155afcb4 100644
--- a/compiler/rustc_metadata/src/rmeta/encoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/encoder.rs
@@ -1712,8 +1712,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
             let stability = tcx.lookup_stability(CRATE_DEF_ID);
             let macros =
                 self.lazy_array(tcx.resolutions(()).proc_macros.iter().map(|p| p.local_def_index));
-            let spans = self.tcx.sess.parse_sess.proc_macro_quoted_spans();
-            for (i, span) in spans.into_iter().enumerate() {
+            for (i, span) in self.tcx.sess.parse_sess.proc_macro_quoted_spans() {
                 let span = self.lazy(span);
                 self.tables.proc_macro_quoted_spans.set_some(i, span);
             }
diff --git a/compiler/rustc_session/src/parse.rs b/compiler/rustc_session/src/parse.rs
index e451668e588..d80911747f3 100644
--- a/compiler/rustc_session/src/parse.rs
+++ b/compiler/rustc_session/src/parse.rs
@@ -8,7 +8,7 @@ use crate::lint::{
 };
 use rustc_ast::node_id::NodeId;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
-use rustc_data_structures::sync::{AtomicBool, Lock, Lrc};
+use rustc_data_structures::sync::{AppendOnlyVec, AtomicBool, Lock, Lrc};
 use rustc_errors::{emitter::SilentEmitter, ColorConfig, Handler};
 use rustc_errors::{
     fallback_fluent_bundle, Diagnostic, DiagnosticBuilder, DiagnosticId, DiagnosticMessage,
@@ -219,7 +219,7 @@ pub struct ParseSess {
     pub assume_incomplete_release: bool,
     /// Spans passed to `proc_macro::quote_span`. Each span has a numerical
     /// identifier represented by its position in the vector.
-    pub proc_macro_quoted_spans: Lock<Vec<Span>>,
+    pub proc_macro_quoted_spans: AppendOnlyVec<Span>,
     /// Used to generate new `AttrId`s. Every `AttrId` is unique.
     pub attr_id_generator: AttrIdGenerator,
 }
@@ -324,13 +324,16 @@ impl ParseSess {
     }
 
     pub fn save_proc_macro_span(&self, span: Span) -> usize {
-        let mut spans = self.proc_macro_quoted_spans.lock();
-        spans.push(span);
-        return spans.len() - 1;
+        self.proc_macro_quoted_spans.push(span)
     }
 
-    pub fn proc_macro_quoted_spans(&self) -> Vec<Span> {
-        self.proc_macro_quoted_spans.lock().clone()
+    pub fn proc_macro_quoted_spans(&self) -> impl Iterator<Item = (usize, Span)> + '_ {
+        // This is equivalent to `.iter().copied().enumerate()`, but that isn't possible for
+        // AppendOnlyVec, so we resort to this scheme.
+        (0..)
+            .map(|i| (i, self.proc_macro_quoted_spans.get(i)))
+            .take_while(|(_, o)| o.is_some())
+            .filter_map(|(i, o)| Some((i, o?)))
     }
 
     #[track_caller]