diff --git a/components/style/stylesheets/keyframes_rule.rs b/components/style/stylesheets/keyframes_rule.rs
index fe52edd60be..aeb9265c549 100644
--- a/components/style/stylesheets/keyframes_rule.rs
+++ b/components/style/stylesheets/keyframes_rule.rs
@@ -145,24 +145,10 @@ impl KeyframePercentage {
 
 /// A keyframes selector is a list of percentages or from/to symbols, which are
 /// converted at parse time to percentages.
-#[derive(Clone, Debug, Eq, PartialEq)]
+#[css(comma, iterable)]
+#[derive(Clone, Debug, Eq, PartialEq, ToCss)]
 pub struct KeyframeSelector(Vec<KeyframePercentage>);
 
-impl ToCss for KeyframeSelector {
-    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
-    where
-        W: Write,
-    {
-        let mut iter = self.0.iter();
-        iter.next().unwrap().to_css(dest)?;
-        for percentage in iter {
-            dest.write_str(", ")?;
-            percentage.to_css(dest)?;
-        }
-        Ok(())
-    }
-}
-
 impl KeyframeSelector {
     /// Return the list of percentages this selector contains.
     #[inline]