diff --git a/servo/components/style/properties/gecko.mako.rs b/servo/components/style/properties/gecko.mako.rs
index 1a35d2f41c38..e45fcb6a23c4 100644
--- a/servo/components/style/properties/gecko.mako.rs
+++ b/servo/components/style/properties/gecko.mako.rs
@@ -2341,7 +2341,7 @@ fn static_assert() {
     pub fn calculate_script_level_size(&self, parent: &Self, device: &Device) -> (Au, Au) {
         use std::cmp;
 
-        let delta = self.gecko.mScriptLevel - parent.gecko.mScriptLevel;
+        let delta = self.gecko.mScriptLevel.saturating_sub(parent.gecko.mScriptLevel);
 
         let parent_size = Au(parent.gecko.mSize);
         let parent_unconstrained_size = Au(parent.gecko.mScriptUnconstrainedSize);
diff --git a/servo/components/style/values/animated/mod.rs b/servo/components/style/values/animated/mod.rs
index 1972d839aff5..1af8f6409e1e 100644
--- a/servo/components/style/values/animated/mod.rs
+++ b/servo/components/style/values/animated/mod.rs
@@ -162,7 +162,7 @@ where
 impl Animate for Au {
     #[inline]
     fn animate(&self, other: &Self, procedure: Procedure) -> Result<Self, ()> {
-        Ok(Au(self.0.animate(&other.0, procedure)?))
+        Ok(Au::new(self.0.animate(&other.0, procedure)?))
     }
 }
 
diff --git a/servo/components/style/values/specified/length.rs b/servo/components/style/values/specified/length.rs
index 3789a5446699..6a0bd08b880f 100644
--- a/servo/components/style/values/specified/length.rs
+++ b/servo/components/style/values/specified/length.rs
@@ -6,7 +6,7 @@
 //!
 //! [length]: https://drafts.csswg.org/css-values/#lengths
 
-use app_units::Au;
+use app_units::{Au, MAX_AU, MIN_AU};
 use cssparser::{Parser, Token, BasicParseError};
 use euclid::Size2D;
 use font_metrics::FontMetricsQueryResult;
@@ -236,16 +236,12 @@ impl CharacterWidth {
     }
 }
 
-/// Same as Gecko
-const ABSOLUTE_LENGTH_MAX: i32 = (1 << 30);
-const ABSOLUTE_LENGTH_MIN: i32 = - (1 << 30);
-
 /// Helper to convert a floating point length to application units
 fn to_au_round(length: CSSFloat, au_per_unit: CSSFloat) -> Au {
     Au(
-        (length * au_per_unit)
-        .min(ABSOLUTE_LENGTH_MAX as f32)
-        .max(ABSOLUTE_LENGTH_MIN as f32)
+        ((length * au_per_unit) as f64)
+        .min(MAX_AU.0 as f64)
+        .max(MIN_AU.0 as f64)
         .round() as i32
     )
 }