diff --git a/servo/components/style/driver.rs b/servo/components/style/driver.rs
index e8dfe7cf3db3..aa39f3482f45 100644
--- a/servo/components/style/driver.rs
+++ b/servo/components/style/driver.rs
@@ -89,7 +89,7 @@ pub fn traverse_dom<E, D>(
     //     ThreadLocalStyleContext on the main thread. If the main thread
     //     ThreadLocalStyleContext has not released its TLS borrow by that point,
     //     we'll panic on double-borrow.
-    let mut maybe_tls: Option<ScopedTLS<ThreadLocalStyleContext<E>>> = None;
+    let mut tls_slots = None;
     let mut tlc = ThreadLocalStyleContext::new(traversal.shared_context());
     let mut context = StyleContext {
         shared: traversal.shared_context(),
@@ -129,7 +129,7 @@ pub fn traverse_dom<E, D>(
             // depth for all the children.
             if pool.is_some() && discovered.len() > WORK_UNIT_MAX {
                 let pool = pool.unwrap();
-                maybe_tls = Some(ScopedTLS::<ThreadLocalStyleContext<E>>::new(pool));
+                let tls = ScopedTLS::<ThreadLocalStyleContext<E>>::new(pool);
                 let root_opaque = root.as_node().opaque();
                 let drain = discovered.drain(..);
                 pool.install(|| {
@@ -151,10 +151,12 @@ pub fn traverse_dom<E, D>(
                             scope,
                             pool,
                             traversal,
-                            maybe_tls.as_ref().unwrap(),
+                            &tls,
                         );
                     });
                 });
+
+                tls_slots = Some(tls.into_slots());
                 break;
             }
             nodes_remaining_at_current_depth = discovered.len();
@@ -164,9 +166,9 @@ pub fn traverse_dom<E, D>(
     // Collect statistics from thread-locals if requested.
     if dump_stats || report_stats {
         let mut aggregate = mem::replace(&mut context.thread_local.statistics, Default::default());
-        let parallel = maybe_tls.is_some();
-        if let Some(tls) = maybe_tls {
-            for mut slot in tls.into_slots().into_vec() {
+        let parallel = tls_slots.is_some();
+        if let Some(ref mut tls) = tls_slots {
+            for slot in tls.iter_mut() {
                 if let Some(cx) = slot.get_mut() {
                     aggregate += cx.statistics.clone();
                 }
diff --git a/servo/components/style/values/computed/font.rs b/servo/components/style/values/computed/font.rs
index a0c4ad695db7..0f821123c203 100644
--- a/servo/components/style/values/computed/font.rs
+++ b/servo/components/style/values/computed/font.rs
@@ -714,10 +714,7 @@ impl FontLanguageOverride {
 
     /// Returns this value as a `&str`, backed by `storage`.
     #[inline]
-    pub fn to_str(self, storage: &mut [u8; 4]) -> &str {
-        if self.0 == 0 {
-            return "normal";
-        }
+    pub(crate) fn to_str(self, storage: &mut [u8; 4]) -> &str {
         *storage = u32::to_be_bytes(self.0);
         // Safe because we ensure it's ASCII during computing
         let slice = if cfg!(debug_assertions) {
@@ -758,6 +755,9 @@ impl ToCss for FontLanguageOverride {
     where
         W: fmt::Write,
     {
+        if self.0 == 0 {
+            return dest.write_str("normal");
+        }
         self.to_str(&mut [0; 4]).to_css(dest)
     }
 }