diff --git a/components/style/properties/longhand/outline.mako.rs b/components/style/properties/longhand/outline.mako.rs
index 73057ab7c33..06b91acbca8 100644
--- a/components/style/properties/longhand/outline.mako.rs
+++ b/components/style/properties/longhand/outline.mako.rs
@@ -11,9 +11,11 @@
 
 // TODO(pcwalton): `invert`
 ${helpers.predefined_type("outline-color", "CSSColor", "::cssparser::Color::CurrentColor",
-                          animatable=True, complex_color=True, need_clone=True)}
+                          animatable=True, complex_color=True, need_clone=True,
+                          spec="https://drafts.csswg.org/css-ui/#propdef-outline-color")}
 
-<%helpers:longhand name="outline-style" need_clone="True" animatable="False">
+<%helpers:longhand name="outline-style" need_clone="True" animatable="False"
+                   spec="https://drafts.csswg.org/css-ui/#propdef-outline-style">
     pub use values::specified::BorderStyle as SpecifiedValue;
     pub fn get_initial_value() -> SpecifiedValue { SpecifiedValue::none }
     pub mod computed_value {
@@ -27,7 +29,8 @@ ${helpers.predefined_type("outline-color", "CSSColor", "::cssparser::Color::Curr
     }
 </%helpers:longhand>
 
-<%helpers:longhand name="outline-width" animatable="True">
+<%helpers:longhand name="outline-width" animatable="True"
+                   spec="https://drafts.csswg.org/css-ui/#propdef-outline-width">
     use app_units::Au;
     use std::fmt;
     use style_traits::ToCss;
@@ -77,9 +80,11 @@ ${helpers.predefined_type("outline-color", "CSSColor", "::cssparser::Color::Curr
 // TODO: Should they animate?
 % for corner in ["topleft", "topright", "bottomright", "bottomleft"]:
     ${helpers.predefined_type("-moz-outline-radius-" + corner, "BorderRadiusSize",
-                              "computed::BorderRadiusSize::zero()",
-                              "parse", products="gecko",
-                              animatable=False)}
+        "computed::BorderRadiusSize::zero()",
+        "parse", products="gecko",
+        animatable=False,
+        spec="Nonstandard (https://developer.mozilla.org/en-US/docs/Web/CSS/-moz-outline-radius)")}
 % endfor
 
-${helpers.predefined_type("outline-offset", "Length", "Au(0)", products="servo", animatable=True)}
+${helpers.predefined_type("outline-offset", "Length", "Au(0)", products="servo", animatable=True,
+                          spec="https://drafts.csswg.org/css-ui/#propdef-outline-offset")}
diff --git a/components/style/properties/shorthand/outline.mako.rs b/components/style/properties/shorthand/outline.mako.rs
index 51d74018124..2fa406e3fca 100644
--- a/components/style/properties/shorthand/outline.mako.rs
+++ b/components/style/properties/shorthand/outline.mako.rs
@@ -4,7 +4,8 @@
 
 <%namespace name="helpers" file="/helpers.mako.rs" />
 
-<%helpers:shorthand name="outline" sub_properties="outline-color outline-style outline-width">
+<%helpers:shorthand name="outline" sub_properties="outline-color outline-style outline-width"
+                    spec="https://drafts.csswg.org/css-ui/#propdef-outline">
     use properties::longhands::outline_width;
     use values::specified;
     use parser::Parse;
@@ -75,7 +76,7 @@
 <%helpers:shorthand name="-moz-outline-radius" sub_properties="${' '.join(
     '-moz-outline-radius-%s' % corner
     for corner in ['topleft', 'topright', 'bottomright', 'bottomleft']
-)}" products="gecko">
+)}" products="gecko" spec="Nonstandard (https://developer.mozilla.org/en-US/docs/Web/CSS/-moz-outline-radius)">
     use properties::shorthands;
 
     pub fn parse_value(context: &ParserContext, input: &mut Parser) -> Result<Longhands, ()> {