diff --git a/components/style/properties/data.py b/components/style/properties/data.py
index 83e91e020b4..f12a7ffd3b3 100644
--- a/components/style/properties/data.py
+++ b/components/style/properties/data.py
@@ -33,10 +33,20 @@ def to_camel_case(ident):
     return re.sub("(^|_|-)([a-z])", lambda m: m.group(2).upper(), ident.strip("_").strip("-"))
 
 
+def parse_aliases(value):
+    aliases = {}
+    for pair in value.split():
+        [a, v] = pair.split("=")
+        aliases[a] = v
+    return aliases
+
+
 class Keyword(object):
     def __init__(self, name, values, gecko_constant_prefix=None,
                  gecko_enum_prefix=None, custom_consts=None,
                  extra_gecko_values=None, extra_servo_values=None,
+                 aliases=None,
+                 extra_gecko_aliases=None, extra_servo_aliases=None,
                  gecko_strip_moz_prefix=True,
                  gecko_inexhaustive=None):
         self.name = name
@@ -48,6 +58,9 @@ class Keyword(object):
         self.gecko_enum_prefix = gecko_enum_prefix
         self.extra_gecko_values = (extra_gecko_values or "").split()
         self.extra_servo_values = (extra_servo_values or "").split()
+        self.aliases = parse_aliases(aliases or "")
+        self.extra_gecko_aliases = parse_aliases(extra_gecko_aliases or "")
+        self.extra_servo_aliases = parse_aliases(extra_servo_aliases or "")
         self.consts_map = {} if custom_consts is None else custom_consts
         self.gecko_strip_moz_prefix = gecko_strip_moz_prefix
         self.gecko_inexhaustive = gecko_inexhaustive or (gecko_enum_prefix is None)
@@ -58,6 +71,16 @@ class Keyword(object):
     def servo_values(self):
         return self.values + self.extra_servo_values
 
+    def gecko_aliases(self):
+        aliases = self.aliases.copy()
+        aliases.update(self.extra_gecko_aliases)
+        return aliases
+
+    def servo_aliases(self):
+        aliases = self.aliases.copy()
+        aliases.update(self.extra_servo_aliases)
+        return aliases
+
     def values_for(self, product):
         if product == "gecko":
             return self.gecko_values()
@@ -66,6 +89,14 @@ class Keyword(object):
         else:
             raise Exception("Bad product: " + product)
 
+    def aliases_for(self, product):
+        if product == "gecko":
+            return self.gecko_aliases()
+        elif product == "servo":
+            return self.servo_aliases()
+        else:
+            raise Exception("Bad product: " + product)
+
     def gecko_constant(self, value):
         moz_stripped = value.replace("-moz-", '') if self.gecko_strip_moz_prefix else value.replace("-moz-", 'moz-')
         mapped = self.consts_map.get(value)
diff --git a/components/style/properties/helpers.mako.rs b/components/style/properties/helpers.mako.rs
index 4b6f20e9d7b..49a751bd59f 100644
--- a/components/style/properties/helpers.mako.rs
+++ b/components/style/properties/helpers.mako.rs
@@ -395,9 +395,33 @@
 
 <%def name="single_keyword(name, values, vector=False, **kwargs)">
     <%call expr="single_keyword_computed(name, values, vector, **kwargs)">
-        use values::computed::ComputedValueAsSpecified;
+        % if not "extra_specified" in kwargs and ("aliases" in kwargs or (("extra_%s_aliases" % product) in kwargs)):
+            impl ToComputedValue for SpecifiedValue {
+                type ComputedValue = computed_value::T;
+
+                #[inline]
+                fn to_computed_value(&self, _context: &Context) -> computed_value::T {
+                    match *self {
+                        % for value in data.longhands_by_name[name].keyword.values_for(product):
+                            SpecifiedValue::${to_rust_ident(value)} => computed_value::T::${to_rust_ident(value)},
+                        % endfor
+                    }
+                }
+                #[inline]
+                fn from_computed_value(computed: &computed_value::T) -> Self {
+                    match *computed {
+                        % for value in data.longhands_by_name[name].keyword.values_for(product):
+                            computed_value::T::${to_rust_ident(value)} => SpecifiedValue::${to_rust_ident(value)},
+                        % endfor
+                    }
+                }
+            }
+        % else:
+            use values::computed::ComputedValueAsSpecified;
+            impl ComputedValueAsSpecified for SpecifiedValue {}
+        % endif
+
         use values::HasViewportPercentage;
-        impl ComputedValueAsSpecified for SpecifiedValue {}
         no_viewport_percentage!(SpecifiedValue);
     </%call>
 </%def>
@@ -444,17 +468,25 @@
         keyword_kwargs = {a: kwargs.pop(a, None) for a in [
             'gecko_constant_prefix', 'gecko_enum_prefix',
             'extra_gecko_values', 'extra_servo_values',
+            'aliases', 'extra_gecko_aliases', 'extra_servo_aliases',
             'custom_consts', 'gecko_inexhaustive',
         ]}
     %>
 
     <%def name="inner_body(keyword, extra_specified=None, needs_conversion=False)">
-        % if extra_specified:
+        % if extra_specified or keyword.aliases_for(product):
             use style_traits::ToCss;
             define_css_keyword_enum! { SpecifiedValue:
-                % for value in keyword.values_for(product) + extra_specified.split():
-                    "${value}" => ${to_rust_ident(value)},
-                % endfor
+                values {
+                    % for value in keyword.values_for(product) + (extra_specified or "").split():
+                        "${value}" => ${to_rust_ident(value)},
+                    % endfor
+                }
+                aliases {
+                    % for alias, value in keyword.aliases_for(product).iteritems():
+                        "${alias}" => ${to_rust_ident(value)},
+                    % endfor
+                }
             }
         % else:
             pub use self::computed_value::T as SpecifiedValue;
@@ -493,6 +525,7 @@
                 conversion_values = keyword.values_for(product)
                 if extra_specified:
                     conversion_values += extra_specified.split()
+                conversion_values += keyword.aliases_for(product).keys()
             %>
             ${gecko_keyword_conversion(keyword, values=conversion_values)}
         % endif
diff --git a/components/style_traits/values.rs b/components/style_traits/values.rs
index 05dab8440f6..663a39fb6ac 100644
--- a/components/style_traits/values.rs
+++ b/components/style_traits/values.rs
@@ -82,20 +82,43 @@ impl_to_css_for_predefined_type!(::cssparser::UnicodeRange);
 
 #[macro_export]
 macro_rules! define_css_keyword_enum {
+    ($name: ident: values { $( $css: expr => $variant: ident),+, }
+                   aliases { $( $alias: expr => $alias_variant: ident ),+, }) => {
+        __define_css_keyword_enum__add_optional_traits!($name [ $( $css => $variant ),+ ]
+                                                              [ $( $alias => $alias_variant ),+ ]);
+    };
+    ($name: ident: values { $( $css: expr => $variant: ident),+, }
+                   aliases { $( $alias: expr => $alias_variant: ident ),* }) => {
+        __define_css_keyword_enum__add_optional_traits!($name [ $( $css => $variant ),+ ]
+                                                              [ $( $alias => $alias_variant ),* ]);
+    };
+    ($name: ident: values { $( $css: expr => $variant: ident),+ }
+                   aliases { $( $alias: expr => $alias_variant: ident ),+, }) => {
+        __define_css_keyword_enum__add_optional_traits!($name [ $( $css => $variant ),+ ]
+                                                              [ $( $alias => $alias_variant ),+ ]);
+    };
+    ($name: ident: values { $( $css: expr => $variant: ident),+ }
+                   aliases { $( $alias: expr => $alias_variant: ident ),* }) => {
+        __define_css_keyword_enum__add_optional_traits!($name [ $( $css => $variant ),+ ]
+                                                              [ $( $alias => $alias_variant ),* ]);
+    };
     ($name: ident: $( $css: expr => $variant: ident ),+,) => {
-        __define_css_keyword_enum__add_optional_traits!($name [ $( $css => $variant ),+ ]);
+        __define_css_keyword_enum__add_optional_traits!($name [ $( $css => $variant ),+ ] []);
     };
     ($name: ident: $( $css: expr => $variant: ident ),+) => {
-        __define_css_keyword_enum__add_optional_traits!($name [ $( $css => $variant ),+ ]);
+        __define_css_keyword_enum__add_optional_traits!($name [ $( $css => $variant ),+ ] []);
     };
 }
 
 #[cfg(feature = "servo")]
 #[macro_export]
 macro_rules! __define_css_keyword_enum__add_optional_traits {
-    ($name: ident [ $( $css: expr => $variant: ident ),+ ]) => {
+    ($name: ident [ $( $css: expr => $variant: ident ),+ ]
+                  [ $( $alias: expr => $alias_variant: ident),* ]) => {
         __define_css_keyword_enum__actual! {
-            $name [ Deserialize, Serialize, HeapSizeOf ] [ $( $css => $variant ),+ ]
+            $name [ Deserialize, Serialize, HeapSizeOf ]
+                  [ $( $css => $variant ),+ ]
+                  [ $( $alias => $alias_variant ),* ]
         }
     };
 }
@@ -103,16 +126,18 @@ macro_rules! __define_css_keyword_enum__add_optional_traits {
 #[cfg(not(feature = "servo"))]
 #[macro_export]
 macro_rules! __define_css_keyword_enum__add_optional_traits {
-    ($name: ident [ $( $css: expr => $variant: ident ),+ ]) => {
+    ($name: ident [ $( $css: expr => $variant: ident ),+ ] [ $( $alias: expr => $alias_variant: ident),* ]) => {
         __define_css_keyword_enum__actual! {
-            $name [] [ $( $css => $variant ),+ ]
+            $name [] [ $( $css => $variant ),+ ] [ $( $alias => $alias_variant ),* ]
         }
     };
 }
 
 #[macro_export]
 macro_rules! __define_css_keyword_enum__actual {
-    ($name: ident [ $( $derived_trait: ident),* ] [ $( $css: expr => $variant: ident ),+ ]) => {
+    ($name: ident [ $( $derived_trait: ident),* ]
+                  [ $( $css: expr => $variant: ident ),+ ]
+                  [ $( $alias: expr => $alias_variant: ident ),* ]) => {
         #[allow(non_camel_case_types, missing_docs)]
         #[derive(Clone, Copy, Debug, Eq, Hash, PartialEq $(, $derived_trait )* )]
         pub enum $name {
@@ -130,6 +155,7 @@ macro_rules! __define_css_keyword_enum__actual {
             pub fn from_ident(ident: &str) -> Result<$name, ()> {
                 match_ignore_ascii_case! { ident,
                                            $( $css => Ok($name::$variant), )+
+                                           $( $alias => Ok($name::$alias_variant), )*
                                            _ => Err(())
                 }
             }