diff --git a/components/style/values/specified/font.rs b/components/style/values/specified/font.rs
index da2fa9432e8..aa56b39336f 100644
--- a/components/style/values/specified/font.rs
+++ b/components/style/values/specified/font.rs
@@ -636,81 +636,31 @@ bitflags! {
     }
 }
 
-#[derive(Clone, Debug, MallocSizeOf, PartialEq)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToCss)]
 /// Set of variant alternates
 pub enum VariantAlternates {
     /// Enables display of stylistic alternates
+    #[css(function)]
     Stylistic(CustomIdent),
     /// Enables display with stylistic sets
+    #[css(comma, function, iterable)]
     Styleset(Box<[CustomIdent]>),
     /// Enables display of specific character variants
+    #[css(comma, function, iterable)]
     CharacterVariant(Box<[CustomIdent]>),
     /// Enables display of swash glyphs
+    #[css(function)]
     Swash(CustomIdent),
     /// Enables replacement of default glyphs with ornaments
+    #[css(function)]
     Ornaments(CustomIdent),
     /// Enables display of alternate annotation forms
+    #[css(function)]
     Annotation(CustomIdent),
     /// Enables display of historical forms
     HistoricalForms,
 }
 
-impl ToCss for VariantAlternates {
-    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
-        match *self {
-            VariantAlternates::Swash(ref atom) => {
-                dest.write_str("swash")?;
-                dest.write_str("(")?;
-                atom.to_css(dest)?;
-                dest.write_str(")")
-            },
-            VariantAlternates::Stylistic(ref atom) => {
-                dest.write_str("stylistic")?;
-                dest.write_str("(")?;
-                atom.to_css(dest)?;
-                dest.write_str(")")
-            },
-            VariantAlternates::Ornaments(ref atom) => {
-                dest.write_str("ornaments")?;
-                dest.write_str("(")?;
-                atom.to_css(dest)?;
-                dest.write_str(")")
-            },
-            VariantAlternates::Annotation(ref atom) => {
-                dest.write_str("annotation")?;
-                dest.write_str("(")?;
-                atom.to_css(dest)?;
-                dest.write_str(")")
-            },
-            VariantAlternates::Styleset(ref vec) => {
-                dest.write_str("styleset")?;
-                dest.write_str("(")?;
-                let mut iter = vec.iter();
-                iter.next().unwrap().to_css(dest)?;
-                for c in iter {
-                    dest.write_str(", ")?;
-                    c.to_css(dest)?;
-                }
-                dest.write_str(")")
-            },
-            VariantAlternates::CharacterVariant(ref vec) => {
-                dest.write_str("character-variant")?;
-                dest.write_str("(")?;
-                let mut iter = vec.iter();
-                iter.next().unwrap().to_css(dest)?;
-                for c in iter {
-                    dest.write_str(", ")?;
-                    c.to_css(dest)?;
-                }
-                dest.write_str(")")
-            },
-            VariantAlternates::HistoricalForms => {
-                dest.write_str("historical-forms")
-            },
-        }
-    }
-}
-
 #[derive(Clone, Debug, MallocSizeOf, PartialEq)]
 /// List of Variant Alternates
 pub struct VariantAlternatesList(pub Box<[VariantAlternates]>);
diff --git a/components/style_derive/to_css.rs b/components/style_derive/to_css.rs
index 6ae438ccbd2..70fb01692a7 100644
--- a/components/style_derive/to_css.rs
+++ b/components/style_derive/to_css.rs
@@ -21,13 +21,27 @@ pub fn derive(input: DeriveInput) -> Tokens {
         let separator = if variant_attrs.comma { ", " } else { " " };
         let mut expr = if !bindings.is_empty() {
             let mut expr = quote! {};
-            for binding in bindings {
-                where_clause.add_trait_bound(&binding.field.ty);
+
+            if variant_attrs.function && variant_attrs.iterable {
+                assert_eq!(bindings.len(), 1);
+                let binding = &bindings[0];
                 expr = quote! {
                     #expr
-                    writer.item(#binding)?;
+
+                    for item in #binding.iter() {
+                        writer.item(item)?;
+                    }
                 };
+            } else {
+                for binding in bindings {
+                    where_clause.add_trait_bound(&binding.field.ty);
+                    expr = quote! {
+                        #expr
+                        writer.item(#binding)?;
+                    };
+                }
             }
+
             quote! {{
                 let mut writer = ::style_traits::values::SequenceWriter::new(&mut *dest, #separator);
                 #expr
@@ -89,6 +103,7 @@ struct CssInputAttrs {
 #[derive(Default, FromVariant)]
 struct CssVariantAttrs {
     function: bool,
+    iterable: bool,
     comma: bool,
 }