diff --git a/components/style/shared_lock.rs b/components/style/shared_lock.rs
index d151062199f0..5bfa7d19737e 100644
--- a/components/style/shared_lock.rs
+++ b/components/style/shared_lock.rs
@@ -258,6 +258,8 @@ impl<T> Locked<T> {
 #[cfg(feature = "gecko")]
 impl<T: ToShmem> ToShmem for Locked<T> {
     fn to_shmem(&self, builder: &mut SharedMemoryBuilder) -> to_shmem::Result<Self> {
+        use std::mem::ManuallyDrop;
+
         let guard = self.shared_lock.read();
         Ok(ManuallyDrop::new(Locked {
             shared_lock: SharedRwLock::read_only(),
diff --git a/components/style/values/specified/font.rs b/components/style/values/specified/font.rs
index 8ab48bfaf211..6fee8c2e770d 100644
--- a/components/style/values/specified/font.rs
+++ b/components/style/values/specified/font.rs
@@ -498,10 +498,12 @@ impl ToComputedValue for FontStretch {
     ToCss,
     ToResolvedValue,
     ToShmem,
+    Serialize,
+    Deserialize,
 )]
-#[cfg_attr(feature = "servo", derive(Serialize, Deserialize))]
 #[allow(missing_docs)]
-pub enum KeywordSize {
+#[repr(u8)]
+pub enum FontSizeKeyword {
     #[css(keyword = "xx-small")]
     XXSmall,
     XSmall,
@@ -794,6 +796,7 @@ impl FontSizeKeyword {
             FontSizeKeyword::XLarge => medium * 3.0 / 2.0,
             FontSizeKeyword::XXLarge => medium * 2.0,
             FontSizeKeyword::XXXLarge => medium * 3.0,
+            FontSizeKeyword::None => unreachable!(),
         })
     }