diff --git a/components/style/counter_style/mod.rs b/components/style/counter_style/mod.rs
index a2b681dc262..5ca39da05ca 100644
--- a/components/style/counter_style/mod.rs
+++ b/components/style/counter_style/mod.rs
@@ -380,7 +380,7 @@ impl Symbol {
 }
 
 /// https://drafts.csswg.org/css-counter-styles/#counter-style-negative
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, ToCss)]
 pub struct Negative(pub Symbol, pub Option<Symbol>);
 
 impl Parse for Negative {
@@ -392,17 +392,6 @@ impl Parse for Negative {
     }
 }
 
-impl ToCss for Negative {
-    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
-        self.0.to_css(dest)?;
-        if let Some(ref symbol) = self.1 {
-            dest.write_char(' ')?;
-            symbol.to_css(dest)?
-        }
-        Ok(())
-    }
-}
-
 /// https://drafts.csswg.org/css-counter-styles/#counter-style-range
 ///
 /// Empty Vec represents 'auto'