diff --git a/src/components/style/common_types.rs b/src/components/style/common_types.rs
index 0d61ff6c108..723ffa989e3 100644
--- a/src/components/style/common_types.rs
+++ b/src/components/style/common_types.rs
@@ -123,6 +123,35 @@ pub mod specified {
             LengthOrPercentageOrAuto::parse_internal(input, /* negative_ok = */ false)
         }
     }
+
+    #[deriving(Clone)]
+    pub enum LengthOrPercentageOrNone {
+        LPN_Length(Length),
+        LPN_Percentage(CSSFloat),  // [0 .. 100%] maps to [0.0 .. 1.0]
+        LPN_None,
+    }
+    impl LengthOrPercentageOrNone {
+        fn parse_internal(input: &ComponentValue, negative_ok: bool)
+                     -> Option<LengthOrPercentageOrNone> {
+            match input {
+                &Dimension(ref value, ref unit) if negative_ok || value.value >= 0.
+                => Length::parse_dimension(value.value, unit.as_slice()).map(LPN_Length),
+                &ast::Percentage(ref value) if negative_ok || value.value >= 0.
+                => Some(LPN_Percentage(value.value / 100.)),
+                &Number(ref value) if value.value == 0. => Some(LPN_Length(Au_(Au(0)))),
+                &Ident(ref value) if value.eq_ignore_ascii_case("none") => Some(LPN_None),
+                _ => None
+            }
+        }
+        #[inline]
+        pub fn parse(input: &ComponentValue) -> Option<LengthOrPercentageOrNone> {
+            LengthOrPercentageOrNone::parse_internal(input, /* negative_ok = */ true)
+        }
+        #[inline]
+        pub fn parse_non_negative(input: &ComponentValue) -> Option<LengthOrPercentageOrNone> {
+            LengthOrPercentageOrNone::parse_internal(input, /* negative_ok = */ false)
+        }
+    }
 }
 
 pub mod computed {
@@ -185,4 +214,19 @@ pub mod computed {
             specified::LPA_Auto => LPA_Auto,
         }
     }
+
+    #[deriving(Eq, Clone)]
+    pub enum LengthOrPercentageOrNone {
+        LPN_Length(Au),
+        LPN_Percentage(CSSFloat),
+        LPN_None,
+    }
+    pub fn compute_LengthOrPercentageOrNone(value: specified::LengthOrPercentageOrNone,
+                                            context: &Context) -> LengthOrPercentageOrNone {
+        match value {
+            specified::LPN_Length(value) => LPN_Length(compute_Au(value, context)),
+            specified::LPN_Percentage(value) => LPN_Percentage(value),
+            specified::LPN_None => LPN_None,
+        }
+    }
 }
diff --git a/src/components/style/properties.rs.mako b/src/components/style/properties.rs.mako
index c12062e504d..6204a567181 100644
--- a/src/components/style/properties.rs.mako
+++ b/src/components/style/properties.rs.mako
@@ -267,6 +267,13 @@ pub mod longhands {
                       "computed::LPA_Auto",
                       "parse_non_negative")}
 
+    ${predefined_type("min-width", "LengthOrPercentage",
+                      "computed::LP_Length(Au(0))",
+                      "parse_non_negative")}
+    ${predefined_type("max-width", "LengthOrPercentageOrNone",
+                      "computed::LPN_None",
+                      "parse_non_negative")}
+
     <%self:single_component_value name="line-height">
         #[deriving(Clone)]
         pub enum SpecifiedValue {
@@ -1123,5 +1130,6 @@ pub mod computed_values {
     pub use cssparser::RGBA;
     pub use super::common_types::computed::{
         LengthOrPercentage, LP_Length, LP_Percentage,
-        LengthOrPercentageOrAuto, LPA_Length, LPA_Percentage, LPA_Auto};
+        LengthOrPercentageOrAuto, LPA_Length, LPA_Percentage, LPA_Auto,
+        LengthOrPercentageOrNone, LPN_Length, LPN_Percentage, LPN_None};
 }