diff --git a/style/values/computed/length_percentage.rs b/style/values/computed/length_percentage.rs
index 4b7a4b102..ea34c23f8 100644
--- a/style/values/computed/length_percentage.rs
+++ b/style/values/computed/length_percentage.rs
@@ -514,7 +514,7 @@ impl LengthPercentage {
     /// Returns the used value.
     #[inline]
     pub fn to_used_value(&self, containing_length: Au) -> Au {
-        Au::from_f32_px_truncate(self.to_pixel_length(containing_length).px())
+        au_from_f32_px_trunc(self.to_pixel_length(containing_length).px())
     }
 
     /// Returns the used value as CSSPixelLength.
@@ -527,7 +527,7 @@ impl LengthPercentage {
     #[inline]
     pub fn maybe_to_used_value(&self, container_len: Option<Au>) -> Option<Au> {
         self.maybe_percentage_relative_to(container_len.map(Length::from))
-            .map(|p| Au::from_f32_px_truncate(p.px()))
+            .map(|length| au_from_f32_px_trunc(length.px()))
     }
 
     /// If there are special rules for computing percentages in a value (e.g.
@@ -554,6 +554,11 @@ impl LengthPercentage {
     }
 }
 
+fn au_from_f32_px_trunc(px: f32) -> Au {
+    let float = (px * app_units::AU_PER_PX as f32).trunc();
+    Au::from_f64_au(float as f64)
+}
+
 impl PartialEq for LengthPercentage {
     fn eq(&self, other: &Self) -> bool {
         self.unpack() == other.unpack()