diff --git a/Cargo.toml b/Cargo.toml
index f170c84..5f16018 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -17,10 +17,9 @@ repository = "https://github.com/ebfull/pairing"
 [dependencies]
 rand = "0.4"
 byteorder = "1"
-ff = "0.3"
+ff = { version = "0.4", features = ["derive"] }
 
 [features]
 unstable-features = ["expose-arith"]
 expose-arith = []
-u128-support = ["ff/u128-support"]
 default = []
diff --git a/README.md b/README.md
index d71d0c5..bf386de 100644
--- a/README.md
+++ b/README.md
@@ -6,14 +6,6 @@ This is a Rust crate for using pairing-friendly elliptic curves. Currently, only
 
 Bring the `pairing` crate into your project just as you normally would.
 
-If you're using a supported platform and the nightly Rust compiler, you can enable the `u128-support` feature for faster arithmetic.
-
-```toml
-[dependencies.pairing]
-version = "0.14"
-features = ["u128-support"]
-```
-
 ## Security Warnings
 
 This library does not make any guarantees about constant-time operations, memory access patterns, or resistance to side-channel attacks.
diff --git a/src/bls12_381/mod.rs b/src/bls12_381/mod.rs
index c6c13c5..106591e 100644
--- a/src/bls12_381/mod.rs
+++ b/src/bls12_381/mod.rs
@@ -20,7 +20,7 @@ pub use self::fr::{Fr, FrRepr};
 
 use super::{CurveAffine, Engine};
 
-use ff::{BitIterator, Field};
+use ff::{BitIterator, Field, ScalarEngine};
 
 // The BLS parameter x for BLS12-381 is -0xd201000000010000
 const BLS_X: u64 = 0xd201000000010000;
@@ -29,8 +29,11 @@ const BLS_X_IS_NEGATIVE: bool = true;
 #[derive(Clone, Debug)]
 pub struct Bls12;
 
-impl Engine for Bls12 {
+impl ScalarEngine for Bls12 {
     type Fr = Fr;
+}
+
+impl Engine for Bls12 {
     type G1 = G1;
     type G1Affine = G1Affine;
     type G2 = G2;
diff --git a/src/lib.rs b/src/lib.rs
index c3640c4..75af6e2 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -25,17 +25,14 @@ pub mod bls12_381;
 mod wnaf;
 pub use self::wnaf::Wnaf;
 
-use ff::{Field, PrimeField, PrimeFieldDecodingError, PrimeFieldRepr, SqrtField};
+use ff::{Field, PrimeField, PrimeFieldDecodingError, PrimeFieldRepr, ScalarEngine, SqrtField};
 use std::error::Error;
 use std::fmt;
 
 /// An "engine" is a collection of types (fields, elliptic curve groups, etc.)
 /// with well-defined relationships. In particular, the G1/G2 curve groups are
 /// of prime order `r`, and are equipped with a bilinear pairing function.
-pub trait Engine: Sized + 'static + Clone {
-    /// This is the scalar field of the G1/G2 groups.
-    type Fr: PrimeField + SqrtField;
-
+pub trait Engine: ScalarEngine {
     /// The projective representation of an element in G1.
     type G1: CurveProjective<
             Engine = Self,