diff --git a/components/layout/fragment.rs b/components/layout/fragment.rs
index 471548214b3..02b74807ba5 100644
--- a/components/layout/fragment.rs
+++ b/components/layout/fragment.rs
@@ -1520,7 +1520,7 @@ impl Fragment {
                     LengthOrPercentageOrAuto::Calc(calc) => {
                         // TODO(nox): This is probably wrong, because it accounts neither for
                         // clamping (not sure if necessary here) nor percentage.
-                        calc.unclamped_length()
+                        Au::from(calc.unclamped_length())
                     },
                 };
 
diff --git a/components/style/gecko/conversions.rs b/components/style/gecko/conversions.rs
index af3ee5978e2..ac0300fd7d8 100644
--- a/components/style/gecko/conversions.rs
+++ b/components/style/gecko/conversions.rs
@@ -29,7 +29,7 @@ impl From<CalcLengthOrPercentage> for nsStyleCoord_CalcValue {
     fn from(other: CalcLengthOrPercentage) -> nsStyleCoord_CalcValue {
         let has_percentage = other.percentage.is_some();
         nsStyleCoord_CalcValue {
-            mLength: other.unclamped_length().0,
+            mLength: other.unclamped_length().to_i32_au(),
             mPercent: other.percentage.map_or(0., |p| p.0),
             mHasPercent: has_percentage,
         }
@@ -43,7 +43,7 @@ impl From<nsStyleCoord_CalcValue> for CalcLengthOrPercentage {
         } else {
             None
         };
-        Self::new(Au(other.mLength), percentage)
+        Self::new(Au(other.mLength).into(), percentage)
     }
 }
 
diff --git a/components/style/properties/helpers/animated_properties.mako.rs b/components/style/properties/helpers/animated_properties.mako.rs
index 585774da3b7..780047ebf8c 100644
--- a/components/style/properties/helpers/animated_properties.mako.rs
+++ b/components/style/properties/helpers/animated_properties.mako.rs
@@ -2316,7 +2316,7 @@ impl ComputeSquaredDistance for TransformOperation {
                     match *lop {
                         LengthOrPercentage::Length(au) => au.to_f64_px(),
                         LengthOrPercentage::Percentage(_) => 0.,
-                        LengthOrPercentage::Calc(calc) => calc.length().to_f64_px(),
+                        LengthOrPercentage::Calc(calc) => calc.length().px() as f64,
                     }
                 };
 
diff --git a/components/style/values/computed/length.rs b/components/style/values/computed/length.rs
index 5b4b4784de1..696a89ccc9c 100644
--- a/components/style/values/computed/length.rs
+++ b/components/style/values/computed/length.rs
@@ -7,9 +7,9 @@
 use app_units::{Au, AU_PER_PX};
 use ordered_float::NotNaN;
 use std::fmt;
-use std::ops::Add;
+use std::ops::{Add, Neg};
 use style_traits::ToCss;
-use style_traits::values::specified::AllowedLengthType;
+use style_traits::values::specified::AllowedNumericType;
 use super::{Number, ToComputedValue, Context, Percentage};
 use values::{Auto, CSSFloat, Either, ExtremumLength, None_, Normal, specified};
 use values::animated::{Animate, Procedure, ToAnimatedZero};
@@ -55,7 +55,7 @@ impl ToComputedValue for specified::Length {
     fn to_computed_value(&self, context: &Context) -> Self::ComputedValue {
         match *self {
             specified::Length::NoCalc(l) => l.to_computed_value(context),
-            specified::Length::Calc(ref calc) => calc.to_computed_value(context).length().into(),
+            specified::Length::Calc(ref calc) => calc.to_computed_value(context).length(),
         }
     }
 
@@ -70,8 +70,8 @@ impl ToComputedValue for specified::Length {
 #[derive(Clone, Copy, Debug, PartialEq, ToAnimatedZero)]
 pub struct CalcLengthOrPercentage {
     #[animation(constant)]
-    pub clamping_mode: AllowedLengthType,
-    length: Au,
+    pub clamping_mode: AllowedNumericType,
+    length: Length,
     pub percentage: Option<Percentage>,
 }
 
@@ -81,8 +81,7 @@ impl ComputeSquaredDistance for CalcLengthOrPercentage {
         // FIXME(nox): This looks incorrect to me, to add a distance between lengths
         // with a distance between percentages.
         Ok(
-            self.unclamped_length().to_f64_px().compute_squared_distance(
-                &other.unclamped_length().to_f64_px())? +
+            self.unclamped_length().compute_squared_distance(&other.unclamped_length())? +
             self.percentage().compute_squared_distance(&other.percentage())?,
         )
     }
@@ -91,15 +90,15 @@ impl ComputeSquaredDistance for CalcLengthOrPercentage {
 impl CalcLengthOrPercentage {
     /// Returns a new `CalcLengthOrPercentage`.
     #[inline]
-    pub fn new(length: Au, percentage: Option<Percentage>) -> Self {
-        Self::with_clamping_mode(length, percentage, AllowedLengthType::All)
+    pub fn new(length: Length, percentage: Option<Percentage>) -> Self {
+        Self::with_clamping_mode(length, percentage, AllowedNumericType::All)
     }
 
     /// Returns a new `CalcLengthOrPercentage` with a specific clamping mode.
     #[inline]
-    pub fn with_clamping_mode(length: Au,
+    pub fn with_clamping_mode(length: Length,
                               percentage: Option<Percentage>,
-                              clamping_mode: AllowedLengthType)
+                              clamping_mode: AllowedNumericType)
                               -> Self {
         Self {
             clamping_mode: clamping_mode,
@@ -112,20 +111,20 @@ impl CalcLengthOrPercentage {
     ///
     /// Panics in debug mode if a percentage is present in the expression.
     #[inline]
-    pub fn length(&self) -> Au {
+    pub fn length(&self) -> CSSPixelLength {
         debug_assert!(self.percentage.is_none());
         self.length_component()
     }
 
     /// Returns the length component of this `calc()`
     #[inline]
-    pub fn length_component(&self) -> Au {
-        self.clamping_mode.clamp(self.length)
+    pub fn length_component(&self) -> CSSPixelLength {
+        CSSPixelLength::new(self.clamping_mode.clamp(self.length.px()))
     }
 
     /// Returns the `<length>` component of this `calc()`, unclamped.
     #[inline]
-    pub fn unclamped_length(&self) -> Au {
+    pub fn unclamped_length(&self) -> CSSPixelLength {
         self.length
     }
 
@@ -140,9 +139,10 @@ impl CalcLengthOrPercentage {
     pub fn to_used_value(&self, container_len: Option<Au>) -> Option<Au> {
         match (container_len, self.percentage) {
             (Some(len), Some(percent)) => {
-                Some(self.clamping_mode.clamp(self.length + len.scale_by(percent.0)))
+                let pixel = self.length.px() + len.scale_by(percent.0).to_f32_px();
+                Some(Au::from_f32_px(self.clamping_mode.clamp(pixel)))
             },
-            (_, None) => Some(self.length()),
+            (_, None) => Some(Au::from(self.length())),
             _ => None,
         }
     }
@@ -152,10 +152,10 @@ impl From<LengthOrPercentage> for CalcLengthOrPercentage {
     fn from(len: LengthOrPercentage) -> CalcLengthOrPercentage {
         match len {
             LengthOrPercentage::Percentage(this) => {
-                CalcLengthOrPercentage::new(Au(0), Some(this))
+                CalcLengthOrPercentage::new(Length::new(0.), Some(this))
             }
             LengthOrPercentage::Length(this) => {
-                CalcLengthOrPercentage::new(this, None)
+                CalcLengthOrPercentage::new(this.into(), None)
             }
             LengthOrPercentage::Calc(this) => {
                 this
@@ -168,10 +168,10 @@ impl From<LengthOrPercentageOrAuto> for Option<CalcLengthOrPercentage> {
     fn from(len: LengthOrPercentageOrAuto) -> Option<CalcLengthOrPercentage> {
         match len {
             LengthOrPercentageOrAuto::Percentage(this) => {
-                Some(CalcLengthOrPercentage::new(Au(0), Some(this)))
+                Some(CalcLengthOrPercentage::new(Length::new(0.), Some(this)))
             }
             LengthOrPercentageOrAuto::Length(this) => {
-                Some(CalcLengthOrPercentage::new(this, None))
+                Some(CalcLengthOrPercentage::new(this.into(), None))
             }
             LengthOrPercentageOrAuto::Calc(this) => {
                 Some(this)
@@ -187,10 +187,10 @@ impl From<LengthOrPercentageOrNone> for Option<CalcLengthOrPercentage> {
     fn from(len: LengthOrPercentageOrNone) -> Option<CalcLengthOrPercentage> {
         match len {
             LengthOrPercentageOrNone::Percentage(this) => {
-                Some(CalcLengthOrPercentage::new(Au(0), Some(this)))
+                Some(CalcLengthOrPercentage::new(Length::new(0.), Some(this)))
             }
             LengthOrPercentageOrNone::Length(this) => {
-                Some(CalcLengthOrPercentage::new(this, None))
+                Some(CalcLengthOrPercentage::new(this.into(), None))
             }
             LengthOrPercentageOrNone::Calc(this) => {
                 Some(this)
@@ -208,14 +208,14 @@ impl ToCss for CalcLengthOrPercentage {
 
         let (length, percentage) = match (self.length, self.percentage) {
             (l, None) => return l.to_css(dest),
-            (l, Some(p)) if l == Au(0) => return p.to_css(dest),
+            (l, Some(p)) if l.px() == 0. => return p.to_css(dest),
             (l, Some(p)) => (l, p),
         };
 
         dest.write_str("calc(")?;
         percentage.to_css(dest)?;
 
-        dest.write_str(if length < Zero::zero() { " - " } else { " + " })?;
+        dest.write_str(if length.px() < Zero::zero() { " - " } else { " + " })?;
         length.abs().to_css(dest)?;
 
         dest.write_str(")")
@@ -226,11 +226,12 @@ impl specified::CalcLengthOrPercentage {
     /// Compute the value, zooming any absolute units by the zoom function.
     fn to_computed_value_with_zoom<F>(&self, context: &Context, zoom_fn: F,
                                       base_size: FontBaseSize) -> CalcLengthOrPercentage
-        where F: Fn(Au) -> Au {
-        let mut length = Au(0);
+        where F: Fn(Length) -> Length {
+        use std::f32;
+        let mut length = 0.;
 
         if let Some(absolute) = self.absolute {
-            length += zoom_fn(Au::from(absolute.to_computed_value(context)));
+            length += zoom_fn(absolute.to_computed_value(context)).px();
         }
 
         for val in &[self.vw.map(ViewportPercentageLength::Vw),
@@ -239,7 +240,7 @@ impl specified::CalcLengthOrPercentage {
                      self.vmax.map(ViewportPercentageLength::Vmax)] {
             if let Some(val) = *val {
                 let viewport_size = context.viewport_size_for_viewport_unit_resolution();
-                length += Au::from(val.to_computed_value(viewport_size));
+                length += val.to_computed_value(viewport_size).px();
             }
         }
 
@@ -248,20 +249,20 @@ impl specified::CalcLengthOrPercentage {
                      self.ex.map(FontRelativeLength::Ex),
                      self.rem.map(FontRelativeLength::Rem)] {
             if let Some(val) = *val {
-                length += Au::from(val.to_computed_value(context, base_size));
+                length += val.to_computed_value(context, base_size).px();
             }
         }
 
         CalcLengthOrPercentage {
             clamping_mode: self.clamping_mode,
-            length: length,
+            length: Length::new(length.min(f32::MAX).max(f32::MIN)),
             percentage: self.percentage,
         }
     }
 
     /// Compute font-size or line-height taking into account text-zoom if necessary.
     pub fn to_computed_value_zoomed(&self, context: &Context, base_size: FontBaseSize) -> CalcLengthOrPercentage {
-        self.to_computed_value_with_zoom(context, |abs| Au::from(context.maybe_zoom_text(abs.into())), base_size)
+        self.to_computed_value_with_zoom(context, |abs| context.maybe_zoom_text(abs), base_size)
     }
 }
 
@@ -277,7 +278,7 @@ impl ToComputedValue for specified::CalcLengthOrPercentage {
     fn from_computed_value(computed: &CalcLengthOrPercentage) -> Self {
         specified::CalcLengthOrPercentage {
             clamping_mode: computed.clamping_mode,
-            absolute: Some(AbsoluteLength::from_computed_value(&computed.length.into())),
+            absolute: Some(AbsoluteLength::from_computed_value(&computed.length)),
             percentage: computed.percentage,
             ..Default::default()
         }
@@ -368,7 +369,7 @@ impl LengthOrPercentage {
         match *self {
             Length(l) => (l, NotNaN::new(0.0).unwrap()),
             Percentage(p) => (Au(0), NotNaN::new(p.0).unwrap()),
-            Calc(c) => (c.unclamped_length(), NotNaN::new(c.percentage()).unwrap()),
+            Calc(c) => (Au::from(c.unclamped_length()), NotNaN::new(c.percentage()).unwrap()),
         }
     }
 
@@ -690,6 +691,11 @@ impl CSSPixelLength {
     pub fn to_i32_au(&self) -> i32 {
         Au::from(*self).0
     }
+
+    /// Return the absolute value of this length.
+    pub fn abs(self) -> Self {
+        CSSPixelLength::new(self.0.abs())
+    }
 }
 
 impl ToCss for CSSPixelLength {
@@ -700,6 +706,15 @@ impl ToCss for CSSPixelLength {
     }
 }
 
+impl Neg for CSSPixelLength {
+    type Output = Self;
+
+    #[inline]
+    fn neg(self) -> Self {
+        CSSPixelLength::new(-self.0)
+    }
+}
+
 impl From<CSSPixelLength> for Au {
     #[inline]
     fn from(len: CSSPixelLength) -> Self {
diff --git a/components/style/values/computed/transform.rs b/components/style/values/computed/transform.rs
index 48ba575b8a2..8f68be3406f 100644
--- a/components/style/values/computed/transform.rs
+++ b/components/style/values/computed/transform.rs
@@ -74,7 +74,7 @@ impl TransformList {
             match *lop {
                 LengthOrPercentage::Length(au) => au.to_f32_px(),
                 LengthOrPercentage::Percentage(_) => 0.,
-                LengthOrPercentage::Calc(calc) => calc.length().to_f32_px(),
+                LengthOrPercentage::Calc(calc) => calc.length().px(),
             }
         };
 
diff --git a/components/style/values/specified/calc.rs b/components/style/values/specified/calc.rs
index 408a5f4ab5b..32fcadf7d6f 100644
--- a/components/style/values/specified/calc.rs
+++ b/components/style/values/specified/calc.rs
@@ -11,7 +11,7 @@ use parser::ParserContext;
 use std::ascii::AsciiExt;
 use std::fmt;
 use style_traits::{ToCss, ParseError, StyleParseError};
-use style_traits::values::specified::AllowedLengthType;
+use style_traits::values::specified::AllowedNumericType;
 use values::{CSSInteger, CSSFloat};
 use values::computed;
 use values::specified::{Angle, Time};
@@ -67,7 +67,7 @@ pub enum CalcUnit {
 #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
 #[allow(missing_docs)]
 pub struct CalcLengthOrPercentage {
-    pub clamping_mode: AllowedLengthType,
+    pub clamping_mode: AllowedNumericType,
     pub absolute: Option<AbsoluteLength>,
     pub vw: Option<CSSFloat>,
     pub vh: Option<CSSFloat>,
@@ -291,7 +291,7 @@ impl CalcNode {
 
     /// Tries to simplify this expression into a `<length>` or `<percentage`>
     /// value.
-    fn to_length_or_percentage(&self, clamping_mode: AllowedLengthType)
+    fn to_length_or_percentage(&self, clamping_mode: AllowedNumericType)
                                -> Result<CalcLengthOrPercentage, ()> {
         let mut ret = CalcLengthOrPercentage {
             clamping_mode: clamping_mode,
@@ -565,7 +565,7 @@ impl CalcNode {
     pub fn parse_length_or_percentage<'i, 't>(
         context: &ParserContext,
         input: &mut Parser<'i, 't>,
-        clamping_mode: AllowedLengthType
+        clamping_mode: AllowedNumericType
     ) -> Result<CalcLengthOrPercentage, ParseError<'i>> {
         Self::parse(context, input, CalcUnit::LengthOrPercentage)?
             .to_length_or_percentage(clamping_mode)
@@ -586,7 +586,7 @@ impl CalcNode {
     pub fn parse_length<'i, 't>(
         context: &ParserContext,
         input: &mut Parser<'i, 't>,
-        clamping_mode: AllowedLengthType
+        clamping_mode: AllowedNumericType
     ) -> Result<CalcLengthOrPercentage, ParseError<'i>> {
         Self::parse(context, input, CalcUnit::Length)?
             .to_length_or_percentage(clamping_mode)
diff --git a/components/style/values/specified/length.rs b/components/style/values/specified/length.rs
index 8f190fdd072..33bad5d90cc 100644
--- a/components/style/values/specified/length.rs
+++ b/components/style/values/specified/length.rs
@@ -15,7 +15,7 @@ use std::{cmp, fmt, mem};
 use std::ascii::AsciiExt;
 use std::ops::{Add, Mul};
 use style_traits::{ToCss, ParseError, StyleParseError};
-use style_traits::values::specified::AllowedLengthType;
+use style_traits::values::specified::AllowedNumericType;
 use stylesheets::CssRuleType;
 use super::{AllowQuirks, Number, ToComputedValue, Percentage};
 use values::{Auto, CSSFloat, Either, FONT_MEDIUM_PX, None_, Normal};
@@ -642,7 +642,7 @@ impl Length {
     #[inline]
     fn parse_internal<'i, 't>(context: &ParserContext,
                               input: &mut Parser<'i, 't>,
-                              num_context: AllowedLengthType,
+                              num_context: AllowedNumericType,
                               allow_quirks: AllowQuirks)
                               -> Result<Length, ParseError<'i>> {
         // FIXME: remove early returns when lifetimes are non-lexical
@@ -683,7 +683,7 @@ impl Length {
                                              input: &mut Parser<'i, 't>,
                                              allow_quirks: AllowQuirks)
                                              -> Result<Length, ParseError<'i>> {
-        Self::parse_internal(context, input, AllowedLengthType::NonNegative, allow_quirks)
+        Self::parse_internal(context, input, AllowedNumericType::NonNegative, allow_quirks)
     }
 
     /// Get an absolute length from a px value.
@@ -713,7 +713,7 @@ impl Length {
                                 input: &mut Parser<'i, 't>,
                                 allow_quirks: AllowQuirks)
                                 -> Result<Self, ParseError<'i>> {
-        Self::parse_internal(context, input, AllowedLengthType::All, allow_quirks)
+        Self::parse_internal(context, input, AllowedNumericType::All, allow_quirks)
     }
 }
 
@@ -725,7 +725,7 @@ impl<T: Parse> Either<Length, T> {
         if let Ok(v) = input.try(|input| T::parse(context, input)) {
             return Ok(Either::Second(v));
         }
-        Length::parse_internal(context, input, AllowedLengthType::NonNegative, AllowQuirks::No).map(Either::First)
+        Length::parse_internal(context, input, AllowedNumericType::NonNegative, AllowQuirks::No).map(Either::First)
     }
 }
 
@@ -752,7 +752,7 @@ impl<T: Parse> Parse for Either<NonNegativeLength, T> {
         if let Ok(v) = input.try(|input| T::parse(context, input)) {
             return Ok(Either::Second(v));
         }
-        Length::parse_internal(context, input, AllowedLengthType::NonNegative, AllowQuirks::No)
+        Length::parse_internal(context, input, AllowedNumericType::NonNegative, AllowQuirks::No)
             .map(NonNegative::<Length>).map(Either::First)
     }
 }
@@ -836,7 +836,7 @@ impl LengthOrPercentage {
 
     fn parse_internal<'i, 't>(context: &ParserContext,
                               input: &mut Parser<'i, 't>,
-                              num_context: AllowedLengthType,
+                              num_context: AllowedNumericType,
                               allow_quirks: AllowQuirks)
                               -> Result<LengthOrPercentage, ParseError<'i>>
     {
@@ -885,7 +885,7 @@ impl LengthOrPercentage {
                                              input: &mut Parser<'i, 't>,
                                              allow_quirks: AllowQuirks)
                                              -> Result<LengthOrPercentage, ParseError<'i>> {
-        Self::parse_internal(context, input, AllowedLengthType::NonNegative, allow_quirks)
+        Self::parse_internal(context, input, AllowedNumericType::NonNegative, allow_quirks)
     }
 
     /// Parse a length, treating dimensionless numbers as pixels
@@ -946,7 +946,7 @@ impl LengthOrPercentage {
     pub fn parse_quirky<'i, 't>(context: &ParserContext,
                                 input: &mut Parser<'i, 't>,
                                 allow_quirks: AllowQuirks) -> Result<Self, ParseError<'i>> {
-        Self::parse_internal(context, input, AllowedLengthType::All, allow_quirks)
+        Self::parse_internal(context, input, AllowedNumericType::All, allow_quirks)
     }
 }
 
@@ -978,7 +978,7 @@ impl From<computed::Percentage> for LengthOrPercentageOrAuto {
 impl LengthOrPercentageOrAuto {
     fn parse_internal<'i, 't>(context: &ParserContext,
                               input: &mut Parser<'i, 't>,
-                              num_context: AllowedLengthType,
+                              num_context: AllowedNumericType,
                               allow_quirks: AllowQuirks)
                               -> Result<Self, ParseError<'i>> {
         // FIXME: remove early returns when lifetimes are non-lexical
@@ -1030,7 +1030,7 @@ impl LengthOrPercentageOrAuto {
                                              input: &mut Parser<'i, 't>,
                                              allow_quirks: AllowQuirks)
                                              -> Result<Self, ParseError<'i>> {
-        Self::parse_internal(context, input, AllowedLengthType::NonNegative, allow_quirks)
+        Self::parse_internal(context, input, AllowedNumericType::NonNegative, allow_quirks)
     }
 
     /// Returns the `auto` value.
@@ -1063,7 +1063,7 @@ impl LengthOrPercentageOrAuto {
                                 input: &mut Parser<'i, 't>,
                                 allow_quirks: AllowQuirks)
                                 -> Result<Self, ParseError<'i>> {
-        Self::parse_internal(context, input, AllowedLengthType::All, allow_quirks)
+        Self::parse_internal(context, input, AllowedNumericType::All, allow_quirks)
     }
 }
 
@@ -1081,7 +1081,7 @@ pub enum LengthOrPercentageOrNone {
 impl LengthOrPercentageOrNone {
     fn parse_internal<'i, 't>(context: &ParserContext,
                               input: &mut Parser<'i, 't>,
-                              num_context: AllowedLengthType,
+                              num_context: AllowedNumericType,
                               allow_quirks: AllowQuirks)
                               -> Result<LengthOrPercentageOrNone, ParseError<'i>>
     {
@@ -1133,14 +1133,14 @@ impl LengthOrPercentageOrNone {
                                              input: &mut Parser<'i, 't>,
                                              allow_quirks: AllowQuirks)
                                              -> Result<Self, ParseError<'i>> {
-        Self::parse_internal(context, input, AllowedLengthType::NonNegative, allow_quirks)
+        Self::parse_internal(context, input, AllowedNumericType::NonNegative, allow_quirks)
     }
 }
 
 impl Parse for LengthOrPercentageOrNone {
     #[inline]
     fn parse<'i, 't>(context: &ParserContext, input: &mut Parser<'i, 't>) -> Result<Self, ParseError<'i>> {
-        Self::parse_internal(context, input, AllowedLengthType::All, AllowQuirks::No)
+        Self::parse_internal(context, input, AllowedNumericType::All, AllowQuirks::No)
     }
 }
 
diff --git a/components/style/values/specified/position.rs b/components/style/values/specified/position.rs
index fb5e22347e8..942263b2285 100644
--- a/components/style/values/specified/position.rs
+++ b/components/style/values/specified/position.rs
@@ -203,14 +203,15 @@ impl<S: Side> ToComputedValue for PositionComponent<S> {
                 match length.to_computed_value(context) {
                     ComputedLengthOrPercentage::Length(length) => {
                         ComputedLengthOrPercentage::Calc(
-                            CalcLengthOrPercentage::new(-length, Some(Percentage::hundred())))
+                            CalcLengthOrPercentage::new((-length).into(), Some(Percentage::hundred())))
                     },
                     ComputedLengthOrPercentage::Percentage(p) => {
                         ComputedLengthOrPercentage::Percentage(Percentage(1.0 - p.0))
                     },
                     ComputedLengthOrPercentage::Calc(calc) => {
                         let p = Percentage(1. - calc.percentage.map_or(0., |p| p.0));
-                        ComputedLengthOrPercentage::Calc(CalcLengthOrPercentage::new(-calc.unclamped_length(), Some(p)))
+                        let l = -calc.unclamped_length();
+                        ComputedLengthOrPercentage::Calc(CalcLengthOrPercentage::new(l, Some(p)))
                     },
                 }
             },
diff --git a/components/style/values/specified/text.rs b/components/style/values/specified/text.rs
index 3e766fb6f67..ec4e779903e 100644
--- a/components/style/values/specified/text.rs
+++ b/components/style/values/specified/text.rs
@@ -84,7 +84,7 @@ impl ToComputedValue for LineHeight {
 
     #[inline]
     fn to_computed_value(&self, context: &Context) -> Self::ComputedValue {
-        use app_units::Au;
+        use values::computed::NonNegativeLength;
         use values::specified::length::FontBaseSize;
         match *self {
             GenericLineHeight::Normal => {
@@ -119,13 +119,13 @@ impl ToComputedValue for LineHeight {
                                 .to_computed_value(
                                     context,
                                     FontBaseSize::CurrentStyle,
-                                );
+                                ).px();
 
-                        let absolute_length = computed_calc.unclamped_length();
-                        computed_calc
+                        let absolute_length = computed_calc.unclamped_length().px();
+                        let pixel = computed_calc
                             .clamping_mode
-                            .clamp(absolute_length + Au::from(font_relative_length))
-                            .into()
+                            .clamp(absolute_length + font_relative_length);
+                        NonNegativeLength::new(pixel)
                     }
                 };
                 GenericLineHeight::Length(result)
diff --git a/components/style_traits/values.rs b/components/style_traits/values.rs
index 8d669d3496a..6e2d2856901 100644
--- a/components/style_traits/values.rs
+++ b/components/style_traits/values.rs
@@ -469,49 +469,6 @@ macro_rules! __define_css_keyword_enum__actual {
 /// Helper types for the handling of specified values.
 pub mod specified {
     use ParsingMode;
-    use app_units::Au;
-    use std::cmp;
-
-    /// Whether to allow negative lengths or not.
-    #[repr(u8)]
-    #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
-    #[derive(Clone, Copy, Debug, Eq, PartialEq)]
-    pub enum AllowedLengthType {
-        /// Allow all kind of lengths.
-        All,
-        /// Allow only non-negative lengths.
-        NonNegative
-    }
-
-    impl Default for AllowedLengthType {
-        #[inline]
-        fn default() -> Self {
-            AllowedLengthType::All
-        }
-    }
-
-    impl AllowedLengthType {
-        /// Whether value is valid for this allowed length type.
-        #[inline]
-        pub fn is_ok(&self, parsing_mode: ParsingMode, value: f32) -> bool {
-            if parsing_mode.allows_all_numeric_values() {
-                return true;
-            }
-            match *self {
-                AllowedLengthType::All => true,
-                AllowedLengthType::NonNegative => value >= 0.,
-            }
-        }
-
-        /// Clamp the value following the rules of this numeric type.
-        #[inline]
-        pub fn clamp(&self, val: Au) -> Au {
-            match *self {
-                AllowedLengthType::All => val,
-                AllowedLengthType::NonNegative => cmp::max(Au(0), val),
-            }
-        }
-    }
 
     /// Whether to allow negative lengths or not.
     #[repr(u8)]
@@ -526,6 +483,13 @@ pub mod specified {
         AtLeastOne,
     }
 
+    impl Default for AllowedNumericType {
+        #[inline]
+        fn default() -> Self {
+            AllowedNumericType::All
+        }
+    }
+
     impl AllowedNumericType {
         /// Whether the value fits the rules of this numeric type.
         #[inline]
diff --git a/components/style_traits/viewport.rs b/components/style_traits/viewport.rs
index d688f131ccf..fc34209af8a 100644
--- a/components/style_traits/viewport.rs
+++ b/components/style_traits/viewport.rs
@@ -107,7 +107,7 @@ impl Zoom {
     pub fn parse<'i, 't>(input: &mut Parser<'i, 't>) -> Result<Zoom, ParseError<'i>> {
         use PARSING_MODE_DEFAULT;
         use cssparser::Token;
-        use values::specified::AllowedLengthType::NonNegative;
+        use values::specified::AllowedNumericType::NonNegative;
 
         match *input.next()? {
             // TODO: This parse() method should take ParserContext as an
diff --git a/tests/unit/style/animated_properties.rs b/tests/unit/style/animated_properties.rs
index f08c3c81c56..2ed9612faeb 100644
--- a/tests/unit/style/animated_properties.rs
+++ b/tests/unit/style/animated_properties.rs
@@ -90,16 +90,18 @@ fn test_transform_interpolation_on_translate() {
         Length::new(25.),
     )]));
     let to = TransformList(Some(vec![
-        TransformOperation::Translate(LengthOrPercentage::Length(Au(100)),
-                                      LengthOrPercentage::Length(Au(50)),
+        TransformOperation::Translate(LengthOrPercentage::Length(Au::from_px(100)),
+                                      LengthOrPercentage::Length(Au::from_px(50)),
                                       Length::new(75.))]));
     assert_eq!(
         from.animate(&to, Procedure::Interpolate { progress: 0.5 }).unwrap(),
         TransformList(Some(vec![TransformOperation::Translate(
             // calc(50px + 25%)
-            LengthOrPercentage::Calc(CalcLengthOrPercentage::new(Au(50), Some(Percentage(0.25)))),
+            LengthOrPercentage::Calc(CalcLengthOrPercentage::new(Length::new(50.),
+                                                                 Some(Percentage(0.25)))),
             // calc(25px + 50%)
-            LengthOrPercentage::Calc(CalcLengthOrPercentage::new(Au(25), Some(Percentage(0.5)))),
+            LengthOrPercentage::Calc(CalcLengthOrPercentage::new(Length::new(25.),
+                                                                 Some(Percentage(0.5)))),
             Length::new(50.),
         )]))
     );
diff --git a/tests/unit/style/attr.rs b/tests/unit/style/attr.rs
index 8c04de5caa0..9fc56ff82bb 100644
--- a/tests/unit/style/attr.rs
+++ b/tests/unit/style/attr.rs
@@ -8,12 +8,12 @@ use style::values::computed::{CalcLengthOrPercentage, Percentage};
 
 #[test]
 fn test_length_calc() {
-    let calc = CalcLengthOrPercentage::new(Au(10), Some(Percentage(0.2)));
+    let calc = CalcLengthOrPercentage::new(Au(10).into(), Some(Percentage(0.2)));
     assert_eq!(calc.to_used_value(Some(Au(10))), Some(Au(12)));
     assert_eq!(calc.to_used_value(Some(Au(0))), Some(Au(10)));
     assert_eq!(calc.to_used_value(None), None);
 
-    let calc = CalcLengthOrPercentage::new(Au(10), None);
+    let calc = CalcLengthOrPercentage::new(Au(10).into(), None);
     assert_eq!(calc.to_used_value(Some(Au(0))), Some(Au(10)));
     assert_eq!(calc.to_used_value(None), Some(Au(10)));
 }