diff --git a/components/style/gecko/selector_parser.rs b/components/style/gecko/selector_parser.rs
index bbf2142ffc64..26921f9a41b7 100644
--- a/components/style/gecko/selector_parser.rs
+++ b/components/style/gecko/selector_parser.rs
@@ -24,6 +24,9 @@ bitflags! {
     }
 }
 
+/// The type used for storing pseudo-class string arguments.
+pub type PseudoClassStringArg = Box<[u16]>;
+
 macro_rules! pseudo_class_name {
     (bare: [$(($css:expr, $name:ident, $gecko_type:tt, $state:tt, $flags:tt),)*],
      string: [$(($s_css:expr, $s_name:ident, $s_gecko_type:tt, $s_state:tt, $s_flags:tt),)*],
@@ -37,7 +40,7 @@ macro_rules! pseudo_class_name {
             )*
             $(
                 #[doc = $s_css]
-                $s_name(Box<[u16]>),
+                $s_name(PseudoClassStringArg),
             )*
             $(
                 #[doc = $k_css]
diff --git a/components/style/servo/selector_parser.rs b/components/style/servo/selector_parser.rs
index 248efcba7de8..0e18761a027c 100644
--- a/components/style/servo/selector_parser.rs
+++ b/components/style/servo/selector_parser.rs
@@ -160,6 +160,9 @@ impl PseudoElement {
     }
 }
 
+/// The type used for storing pseudo-class string arguments.
+pub type PseudoClassStringArg = Box<str>;
+
 /// A non tree-structural pseudo-class.
 /// See https://drafts.csswg.org/selectors-4/#structural-pseudos
 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
@@ -175,7 +178,7 @@ pub enum NonTSPseudoClass {
     Fullscreen,
     Hover,
     Indeterminate,
-    Lang(Box<str>),
+    Lang(PseudoClassStringArg),
     Link,
     PlaceholderShown,
     ReadWrite,