diff --git a/components/style/values/computed/length.rs b/components/style/values/computed/length.rs
index 94fd0bc12a0..535219d187d 100644
--- a/components/style/values/computed/length.rs
+++ b/components/style/values/computed/length.rs
@@ -277,6 +277,7 @@ impl ToComputedValue for specified::CalcLengthOrPercentage {
 #[allow(missing_docs)]
 #[animate(fallback = "Self::animate_fallback")]
 #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
+#[css(derive_debug)]
 #[derive(Animate, Clone, Copy, PartialEq, ToAnimatedZero, ToCss)]
 pub enum LengthOrPercentage {
     Length(Au),
@@ -391,16 +392,6 @@ impl LengthOrPercentage {
     }
 }
 
-impl fmt::Debug for LengthOrPercentage {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match *self {
-            LengthOrPercentage::Length(length) => write!(f, "{:?}", length),
-            LengthOrPercentage::Percentage(percentage) => write!(f, "{}%", percentage.0 * 100.),
-            LengthOrPercentage::Calc(calc) => write!(f, "{:?}", calc),
-        }
-    }
-}
-
 impl ToComputedValue for specified::LengthOrPercentage {
     type ComputedValue = LengthOrPercentage;
 
@@ -440,6 +431,7 @@ impl ToComputedValue for specified::LengthOrPercentage {
 #[allow(missing_docs)]
 #[animate(fallback = "Self::animate_fallback")]
 #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
+#[css(derive_debug)]
 #[derive(Animate, Clone, Copy, PartialEq, ToCss)]
 pub enum LengthOrPercentageOrAuto {
     Length(Au),
@@ -495,17 +487,6 @@ impl LengthOrPercentageOrAuto {
     }
 }
 
-impl fmt::Debug for LengthOrPercentageOrAuto {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match *self {
-            LengthOrPercentageOrAuto::Length(length) => write!(f, "{:?}", length),
-            LengthOrPercentageOrAuto::Percentage(percentage) => write!(f, "{}%", percentage.0 * 100.),
-            LengthOrPercentageOrAuto::Auto => write!(f, "auto"),
-            LengthOrPercentageOrAuto::Calc(calc) => write!(f, "{:?}", calc),
-        }
-    }
-}
-
 impl ToComputedValue for specified::LengthOrPercentageOrAuto {
     type ComputedValue = LengthOrPercentageOrAuto;
 
@@ -551,6 +532,7 @@ impl ToComputedValue for specified::LengthOrPercentageOrAuto {
 #[allow(missing_docs)]
 #[animate(fallback = "Self::animate_fallback")]
 #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
+#[css(derive_debug)]
 #[derive(Animate, Clone, Copy, PartialEq, ToCss)]
 pub enum LengthOrPercentageOrNone {
     Length(Au),
@@ -603,17 +585,6 @@ impl LengthOrPercentageOrNone {
     }
 }
 
-impl fmt::Debug for LengthOrPercentageOrNone {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match *self {
-            LengthOrPercentageOrNone::Length(length) => write!(f, "{:?}", length),
-            LengthOrPercentageOrNone::Percentage(percentage) => write!(f, "{}%", percentage.0 * 100.),
-            LengthOrPercentageOrNone::Calc(calc) => write!(f, "{:?}", calc),
-            LengthOrPercentageOrNone::None => write!(f, "none"),
-        }
-    }
-}
-
 impl ToComputedValue for specified::LengthOrPercentageOrNone {
     type ComputedValue = LengthOrPercentageOrNone;
 
diff --git a/components/style_derive/to_css.rs b/components/style_derive/to_css.rs
index bd66b9b8caa..6ae438ccbd2 100644
--- a/components/style_derive/to_css.rs
+++ b/components/style_derive/to_css.rs
@@ -3,21 +3,22 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use cg;
-use quote;
-use syn;
+use quote::Tokens;
+use syn::DeriveInput;
 use synstructure;
 
-pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
+pub fn derive(input: DeriveInput) -> Tokens {
     let name = &input.ident;
     let trait_path = &["style_traits", "ToCss"];
     let (impl_generics, ty_generics, mut where_clause) =
         cg::trait_parts(&input, trait_path);
 
+    let input_attrs = cg::parse_input_attrs::<CssInputAttrs>(&input);
     let style = synstructure::BindStyle::Ref.into();
     let match_body = synstructure::each_variant(&input, &style, |bindings, variant| {
         let mut identifier = to_css_identifier(variant.ident.as_ref());
-        let css_attrs = cg::parse_variant_attrs::<CssAttrs>(variant);
-        let separator = if css_attrs.comma { ", " } else { " " };
+        let variant_attrs = cg::parse_variant_attrs::<CssVariantAttrs>(variant);
+        let separator = if variant_attrs.comma { ", " } else { " " };
         let mut expr = if !bindings.is_empty() {
             let mut expr = quote! {};
             for binding in bindings {
@@ -37,7 +38,7 @@ pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
                 ::std::fmt::Write::write_str(dest, #identifier)
             }
         };
-        if css_attrs.function {
+        if variant_attrs.function {
             identifier.push_str("(");
             expr = quote! {
                 ::std::fmt::Write::write_str(dest, #identifier)?;
@@ -48,7 +49,7 @@ pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
         Some(expr)
     });
 
-    quote! {
+    let mut impls = quote! {
         impl #impl_generics ::style_traits::ToCss for #name #ty_generics #where_clause {
             #[allow(unused_variables)]
             #[inline]
@@ -61,12 +62,32 @@ pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
                 }
             }
         }
+    };
+
+    if input_attrs.derive_debug {
+        impls.append(quote! {
+            impl #impl_generics ::std::fmt::Debug for #name #ty_generics #where_clause {
+                fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
+                    ::style_traits::ToCss::to_css(self, f)
+                }
+            }
+        });
     }
+
+    impls
 }
 
-#[derive(Default, FromVariant)]
 #[darling(attributes(css), default)]
-struct CssAttrs {
+#[derive(Default, FromDeriveInput)]
+struct CssInputAttrs {
+    derive_debug: bool,
+    function: bool,
+    comma: bool,
+}
+
+#[darling(attributes(css), default)]
+#[derive(Default, FromVariant)]
+struct CssVariantAttrs {
     function: bool,
     comma: bool,
 }