diff --git a/Cargo.lock b/Cargo.lock
index b1e23405138..814337eed4d 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1930,6 +1930,7 @@ dependencies = [
  "malloc_size_of 0.0.1",
  "msg 0.0.1",
  "net_traits 0.0.1",
+ "num-traits 0.2.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "ordered-float 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "parking_lot 0.6.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "profile_traits 0.0.1",
diff --git a/components/layout/Cargo.toml b/components/layout/Cargo.toml
index 9a960b51305..06de13c951f 100644
--- a/components/layout/Cargo.toml
+++ b/components/layout/Cargo.toml
@@ -29,6 +29,7 @@ log = "0.4"
 malloc_size_of = { path = "../malloc_size_of" }
 msg = {path = "../msg"}
 net_traits = {path = "../net_traits"}
+num-traits = "0.2"
 ordered-float = "1.0"
 parking_lot = "0.6"
 profile_traits = {path = "../profile_traits"}
diff --git a/components/layout/flow.rs b/components/layout/flow.rs
index 4bf7622636c..b25d3ba028d 100644
--- a/components/layout/flow.rs
+++ b/components/layout/flow.rs
@@ -49,6 +49,7 @@ use crate::table_wrapper::TableWrapperFlow;
 use euclid::{Point2D, Rect, Size2D, Vector2D};
 use gfx_traits::print_tree::PrintTree;
 use gfx_traits::StackingContextId;
+use num_traits::cast::FromPrimitive;
 use serde::ser::{Serialize, SerializeStruct, Serializer};
 use servo_geometry::{au_rect_to_f32_rect, f32_rect_to_au_rect, MaxRect};
 use std::fmt;