diff --git a/Cargo.lock b/Cargo.lock
index fb1e0982b0ba..7064a3229513 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -57,7 +57,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
 name = "app_units"
-version = "0.5.3"
+version = "0.5.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "heapsize 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1091,7 +1091,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 name = "gfx"
 version = "0.0.1"
 dependencies = [
- "app_units 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "app_units 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "bitflags 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "byteorder 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "core-foundation 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1504,7 +1504,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 name = "layout"
 version = "0.0.1"
 dependencies = [
- "app_units 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "app_units 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "atomic_refcell 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "bitflags 0.8.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "canvas_traits 0.0.1",
@@ -1554,7 +1554,7 @@ dependencies = [
 name = "layout_thread"
 version = "0.0.1"
 dependencies = [
- "app_units 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "app_units 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "atomic_refcell 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "euclid 0.15.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "fnv 1.0.5 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -2528,7 +2528,7 @@ name = "script"
 version = "0.0.1"
 dependencies = [
  "angle 0.5.0 (git+https://github.com/servo/angle?branch=servo)",
- "app_units 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "app_units 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "audio-video-metadata 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "base64 0.5.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "bitflags 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -2607,7 +2607,7 @@ dependencies = [
 name = "script_layout_interface"
 version = "0.0.1"
 dependencies = [
- "app_units 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "app_units 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "atomic_refcell 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "canvas_traits 0.0.1",
  "cssparser 0.20.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -2916,7 +2916,7 @@ dependencies = [
 name = "servo_geometry"
 version = "0.0.1"
 dependencies = [
- "app_units 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "app_units 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "euclid 0.15.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "heapsize 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
@@ -3072,7 +3072,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 name = "style"
 version = "0.0.1"
 dependencies = [
- "app_units 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "app_units 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "arraydeque 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "arrayvec 0.3.23 (registry+https://github.com/rust-lang/crates.io-index)",
  "atomic_refcell 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -3136,7 +3136,7 @@ dependencies = [
 name = "style_tests"
 version = "0.0.1"
 dependencies = [
- "app_units 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "app_units 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "byteorder 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "cssparser 0.20.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "euclid 0.15.1 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -3158,7 +3158,7 @@ dependencies = [
 name = "style_traits"
 version = "0.0.1"
 dependencies = [
- "app_units 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "app_units 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "bitflags 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "cssparser 0.20.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "euclid 0.15.1 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -3550,7 +3550,7 @@ name = "webrender"
 version = "0.50.0"
 source = "git+https://github.com/servo/webrender#e7c60ad67ca9c0732be18c3df25b686f12d652ca"
 dependencies = [
- "app_units 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "app_units 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "bincode 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "bit-set 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "bitflags 0.9.1 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -3578,7 +3578,7 @@ name = "webrender_api"
 version = "0.50.0"
 source = "git+https://github.com/servo/webrender#e7c60ad67ca9c0732be18c3df25b686f12d652ca"
 dependencies = [
- "app_units 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "app_units 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "bincode 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "byteorder 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "core-foundation 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -3716,7 +3716,7 @@ dependencies = [
 "checksum angle 0.5.0 (git+https://github.com/servo/angle?branch=servo)" = "<none>"
 "checksum ansi_term 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)" = "23ac7c30002a5accbf7e8987d0632fa6de155b7c3d39d0067317a391e00a2ef6"
 "checksum antidote 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "34fde25430d87a9388dadbe6e34d7f72a462c8b43ac8d309b42b0a8505d7e2a5"
-"checksum app_units 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)" = "7ff4f3fe57393a150b39b026b6f6f4b9a6c4f49b52d0a4e2d61d08d926358438"
+"checksum app_units 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)" = "7eb1573f29213263e6016754100e0ae875049d3692dfe6764834c2d7957ca94c"
 "checksum arraydeque 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)" = "96e774cadb24c2245225280c6799793f9802b918a58a79615e9490607489a717"
 "checksum arrayvec 0.3.23 (registry+https://github.com/rust-lang/crates.io-index)" = "699e63a93b79d717e8c3b5eb1b28b7780d0d6d9e59a72eb769291c83b0c8dc67"
 "checksum aster 0.41.0 (registry+https://github.com/rust-lang/crates.io-index)" = "4ccfdf7355d9db158df68f976ed030ab0f6578af811f5a7bb6dcf221ec24e0e0"
diff --git a/components/style/Cargo.toml b/components/style/Cargo.toml
index b97002f3c4d8..196fccf47786 100644
--- a/components/style/Cargo.toml
+++ b/components/style/Cargo.toml
@@ -29,7 +29,7 @@ servo = ["serde", "heapsize", "heapsize_derive",
 gecko_debug = ["nsstring_vendor/gecko_debug"]
 
 [dependencies]
-app_units = "0.5.3"
+app_units = "0.5.5"
 arrayvec = "0.3.20"
 arraydeque = "0.2.3"
 atomic_refcell = "0.1"
diff --git a/components/style/values/specified/length.rs b/components/style/values/specified/length.rs
index 6a0bd08b880f..6f20b801a2a1 100644
--- a/components/style/values/specified/length.rs
+++ b/components/style/values/specified/length.rs
@@ -6,7 +6,7 @@
 //!
 //! [length]: https://drafts.csswg.org/css-values/#lengths
 
-use app_units::{Au, MAX_AU, MIN_AU};
+use app_units::Au;
 use cssparser::{Parser, Token, BasicParseError};
 use euclid::Size2D;
 use font_metrics::FontMetricsQueryResult;
@@ -236,16 +236,6 @@ impl CharacterWidth {
     }
 }
 
-/// 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) as f64)
-        .min(MAX_AU.0 as f64)
-        .max(MIN_AU.0 as f64)
-        .round() as i32
-    )
-}
-
 /// Represents an absolute length with its unit
 #[derive(Clone, Copy, Debug, PartialEq)]
 #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
@@ -292,16 +282,20 @@ impl ToComputedValue for AbsoluteLength {
     }
 }
 
+fn au_from_f32_round(x: f32) -> Au {
+    Au::from_f64_au((x as f64).round())
+}
+
 impl From<AbsoluteLength> for Au {
     fn from(length: AbsoluteLength) -> Au {
         match length {
-            AbsoluteLength::Px(value) => to_au_round(value, AU_PER_PX),
-            AbsoluteLength::In(value) => to_au_round(value, AU_PER_IN),
-            AbsoluteLength::Cm(value) => to_au_round(value, AU_PER_CM),
-            AbsoluteLength::Mm(value) => to_au_round(value, AU_PER_MM),
-            AbsoluteLength::Q(value) => to_au_round(value, AU_PER_Q),
-            AbsoluteLength::Pt(value) => to_au_round(value, AU_PER_PT),
-            AbsoluteLength::Pc(value) => to_au_round(value, AU_PER_PC),
+            AbsoluteLength::Px(value) => au_from_f32_round((value * AU_PER_PX)),
+            AbsoluteLength::In(value) => au_from_f32_round((value * AU_PER_IN)),
+            AbsoluteLength::Cm(value) => au_from_f32_round((value * AU_PER_CM)),
+            AbsoluteLength::Mm(value) => au_from_f32_round((value * AU_PER_MM)),
+            AbsoluteLength::Q(value) => au_from_f32_round((value * AU_PER_Q)),
+            AbsoluteLength::Pt(value) => au_from_f32_round((value * AU_PER_PT)),
+            AbsoluteLength::Pc(value) => au_from_f32_round((value * AU_PER_PC)),
         }
     }
 }
@@ -360,7 +354,7 @@ impl PhysicalLength {
 
         let inch = self.0 / MM_PER_INCH;
 
-        to_au_round(inch, physical_inch as f32)
+        au_from_f32_round(inch * physical_inch as f32)
     }
 }