diff --git a/Cargo.lock b/Cargo.lock
index cc8c7d3c7..92d3bd5c5 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1580,7 +1580,7 @@ version = "0.1.0"
 dependencies = [
  "byteorder 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "ethabi 2.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "ethcore-util 1.8.0",
+ "ethcore-bigint 0.1.3",
  "futures 0.1.11 (registry+https://github.com/rust-lang/crates.io-index)",
  "native-contract-generator 0.1.0",
 ]
diff --git a/ethcore/native_contracts/Cargo.toml b/ethcore/native_contracts/Cargo.toml
index 5dc18c8f5..2f91a4848 100644
--- a/ethcore/native_contracts/Cargo.toml
+++ b/ethcore/native_contracts/Cargo.toml
@@ -9,7 +9,7 @@ build = "build.rs"
 ethabi = "2.0"
 futures = "0.1"
 byteorder = "1.0"
-ethcore-util = { path = "../../util" }
+ethcore-bigint = { path = "../../util/bigint" }
 
 [build-dependencies]
 native-contract-generator = { path = "generator" }
diff --git a/ethcore/native_contracts/generator/src/lib.rs b/ethcore/native_contracts/generator/src/lib.rs
index 793ad6085..996ee4969 100644
--- a/ethcore/native_contracts/generator/src/lib.rs
+++ b/ethcore/native_contracts/generator/src/lib.rs
@@ -15,7 +15,7 @@
 // along with Parity.  If not, see <http://www.gnu.org/licenses/>.
 
 //! Rust code contract generator.
-//! The code generated will require a dependence on the `ethcore-util`,
+//! The code generated will require a dependence on the `ethcore-bigint::prelude`,
 //! `ethabi`, `byteorder`, and `futures` crates.
 //! This currently isn't hygienic, so compilation of generated code may fail
 //! due to missing crates or name collisions. This will change when
@@ -48,14 +48,14 @@ pub fn generate_module(struct_name: &str, abi: &str) -> Result<String, Error> {
 use byteorder::{{BigEndian, ByteOrder}};
 use futures::{{future, Future, IntoFuture, BoxFuture}};
 use ethabi::{{Contract, Interface, Token, Event}};
-use util;
+use bigint;
 
 /// Generated Rust bindings to an Ethereum contract.
 #[derive(Clone, Debug)]
 pub struct {name} {{
 	contract: Contract,
 	/// Address to make calls to.
-	pub address: util::Address,
+	pub address: bigint::prelude::H160,
 }}
 
 const ABI: &'static str = r#"{abi_str}"#;
@@ -63,7 +63,7 @@ const ABI: &'static str = r#"{abi_str}"#;
 impl {name} {{
 	/// Create a new instance of `{name}` with an address.
 	/// Calls can be made, given a callback for dispatching calls asynchronously.
-	pub fn new(address: util::Address) -> Self {{
+	pub fn new(address: bigint::prelude::H160) -> Self {{
 		let contract = Contract::new(Interface::load(ABI.as_bytes())
 			.expect("ABI checked at generation-time; qed"));
 		{name} {{
@@ -108,7 +108,7 @@ fn generate_functions(contract: &Contract) -> Result<String, Error> {
 /// Outputs: {abi_outputs:?}
 pub fn {snake_name}<F, U>(&self, call: F, {params}) -> BoxFuture<{output_type}, String>
 	where
-	    F: FnOnce(util::Address, Vec<u8>) -> U,
+	    F: FnOnce(bigint::prelude::H160, Vec<u8>) -> U,
 	    U: IntoFuture<Item=Vec<u8>, Error=String>,
 		U::Future: Send + 'static
 {{
@@ -217,8 +217,8 @@ fn output_params_codegen(outputs: &[ParamType]) -> Result<(String, String), Para
 // create code for an argument type from param type.
 fn rust_type(input: ParamType) -> Result<String, ParamType> {
 	Ok(match input {
-		ParamType::Address => "util::Address".into(),
-		ParamType::FixedBytes(len) if len <= 32 => format!("util::H{}", len * 8),
+		ParamType::Address => "bigint::prelude::H160".into(),
+		ParamType::FixedBytes(len) if len <= 32 => format!("bigint::prelude::H{}", len * 8),
 		ParamType::Bytes | ParamType::FixedBytes(_) => "Vec<u8>".into(),
 		ParamType::Int(width) => match width {
 			8 | 16 | 32 | 64 => format!("i{}", width),
@@ -226,7 +226,7 @@ fn rust_type(input: ParamType) -> Result<String, ParamType> {
 		},
 		ParamType::Uint(width) => match width {
 			8 | 16 | 32 | 64 => format!("u{}", width),
-			128 | 160 | 256 => format!("util::U{}", width),
+			128 | 160 | 256 => format!("bigint::prelude::U{}", width),
 			_ => return Err(ParamType::Uint(width)),
 		},
 		ParamType::Bool => "bool".into(),
@@ -259,8 +259,8 @@ fn tokenize(name: &str, input: ParamType) -> (bool, String) {
 		},
 		ParamType::Uint(width) => format!(
 			"let mut r = [0; 32]; {}.to_big_endian(&mut r); Token::Uint(r)",
-			if width <= 64 { format!("util::U256::from({} as u64)", name) }
-			else { format!("util::U256::from({})", name) }
+			if width <= 64 { format!("bigint::prelude::U256::from({} as u64)", name) }
+			else { format!("bigint::prelude::U256::from({})", name) }
 		),
 		ParamType::Bool => format!("Token::Bool({})", name),
 		ParamType::String => format!("Token::String({})", name),
@@ -281,11 +281,11 @@ fn tokenize(name: &str, input: ParamType) -> (bool, String) {
 // panics on unsupported types.
 fn detokenize(name: &str, output_type: ParamType) -> String {
 	match output_type {
-		ParamType::Address => format!("{}.to_address().map(util::H160)", name),
+		ParamType::Address => format!("{}.to_address().map(bigint::prelude::H160)", name),
 		ParamType::Bytes => format!("{}.to_bytes()", name),
 		ParamType::FixedBytes(len) if len <= 32 => {
 			// ensure no panic on slice too small.
-			let read_hash = format!("b.resize({}, 0); util::H{}::from_slice(&b[..{}])",
+			let read_hash = format!("b.resize({}, 0); bigint::prelude::H{}::from_slice(&b[..{}])",
 				len, len * 8, len);
 
 			format!("{}.to_fixed_bytes().map(|mut b| {{ {} }})",
@@ -302,8 +302,8 @@ fn detokenize(name: &str, output_type: ParamType) -> String {
 		}
 		ParamType::Uint(width) => {
 			let read_uint = match width {
-				8 | 16 | 32 | 64 => format!("util::U256(u).low_u64() as u{}", width),
-				_ => format!("util::U{}::from(&u[..])", width),
+				8 | 16 | 32 | 64 => format!("bigint::prelude::U256(u).low_u64() as u{}", width),
+				_ => format!("bigint::prelude::U{}::from(&u[..])", width),
 			};
 
 			format!("{}.to_uint().map(|u| {})", name, read_uint)
@@ -328,30 +328,30 @@ mod tests {
 	#[test]
 	fn input_types() {
 		assert_eq!(::input_params_codegen(&[]).unwrap().0, "");
-		assert_eq!(::input_params_codegen(&[ParamType::Address]).unwrap().0, "param_0: util::Address, ");
+		assert_eq!(::input_params_codegen(&[ParamType::Address]).unwrap().0, "param_0: bigint::prelude::H160, ");
 		assert_eq!(::input_params_codegen(&[ParamType::Address, ParamType::Bytes]).unwrap().0,
-			"param_0: util::Address, param_1: Vec<u8>, ");
+			"param_0: bigint::prelude::H160, param_1: Vec<u8>, ");
 	}
 
 	#[test]
 	fn output_types() {
 		assert_eq!(::output_params_codegen(&[]).unwrap().0, "()");
-		assert_eq!(::output_params_codegen(&[ParamType::Address]).unwrap().0, "(util::Address)");
+		assert_eq!(::output_params_codegen(&[ParamType::Address]).unwrap().0, "(bigint::prelude::H160)");
 		assert_eq!(::output_params_codegen(&[ParamType::Address, ParamType::Array(Box::new(ParamType::Bytes))]).unwrap().0,
-			"(util::Address, Vec<Vec<u8>>)");
+			"(bigint::prelude::H160, Vec<Vec<u8>>)");
 	}
 
 	#[test]
 	fn rust_type() {
-		assert_eq!(::rust_type(ParamType::FixedBytes(32)).unwrap(), "util::H256");
+		assert_eq!(::rust_type(ParamType::FixedBytes(32)).unwrap(), "bigint::prelude::H256");
 		assert_eq!(::rust_type(ParamType::Array(Box::new(ParamType::FixedBytes(32)))).unwrap(),
-			"Vec<util::H256>");
+			"Vec<bigint::prelude::H256>");
 
 		assert_eq!(::rust_type(ParamType::Uint(64)).unwrap(), "u64");
 		assert!(::rust_type(ParamType::Uint(63)).is_err());
 
 		assert_eq!(::rust_type(ParamType::Int(32)).unwrap(), "i32");
-		assert_eq!(::rust_type(ParamType::Uint(256)).unwrap(), "util::U256");
+		assert_eq!(::rust_type(ParamType::Uint(256)).unwrap(), "bigint::prelude::U256");
 	}
 
 	// codegen tests will need bootstrapping of some kind.
diff --git a/ethcore/native_contracts/src/lib.rs b/ethcore/native_contracts/src/lib.rs
index e35a4ec19..9b73ace79 100644
--- a/ethcore/native_contracts/src/lib.rs
+++ b/ethcore/native_contracts/src/lib.rs
@@ -21,7 +21,7 @@
 extern crate futures;
 extern crate byteorder;
 extern crate ethabi;
-extern crate ethcore_util as util;
+extern crate ethcore_bigint as bigint;
 
 mod registry;
 mod urlhint;