diff --git a/ethereum-types/src/lib.rs b/ethereum-types/src/lib.rs
index c10128b..62229c2 100644
--- a/ethereum-types/src/lib.rs
+++ b/ethereum-types/src/lib.rs
@@ -1,5 +1,7 @@
 #![cfg_attr(not(feature="std"), no_std)]
 
+#![cfg_attr(asm_available, feature(asm))]
+
 #[cfg(feature="std")]
 extern crate core;
 #[macro_use]
diff --git a/ethereum-types/src/uint.rs b/ethereum-types/src/uint.rs
index f1595ad..6b12c8a 100644
--- a/ethereum-types/src/uint.rs
+++ b/ethereum-types/src/uint.rs
@@ -7,7 +7,6 @@ impl U256 {
 	/// No overflow possible
 	#[cfg(all(asm_available, target_arch="x86_64"))]
 	pub fn full_mul(self, other: U256) -> U512 {
-		#![feature(asm)]
 		let self_t: &[u64; 4] = &self.0;
 		let other_t: &[u64; 4] = &other.0;
 		let mut result: [u64; 8] = unsafe { ::core::mem::uninitialized() };
diff --git a/tests/Cargo.toml b/tests/Cargo.toml
index 6734e37..4450162 100644
--- a/tests/Cargo.toml
+++ b/tests/Cargo.toml
@@ -3,6 +3,9 @@ name = "tests"
 version = "0.1.0"
 authors = ["debris <marek.kotewicz@gmail.com>"]
 
+[build-dependencies]
+rustc_version = "0.2"
+
 [dependencies]
 crunchy = "0.1.5"
 ethereum-types = { path ="../ethereum-types", features = ["std", "heapsizeof"] }
diff --git a/tests/build.rs b/tests/build.rs
new file mode 100644
index 0000000..432acc3
--- /dev/null
+++ b/tests/build.rs
@@ -0,0 +1,17 @@
+// Copyright 2015-2017 Parity Technologies
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+extern crate rustc_version;
+
+use rustc_version::{version_meta, Channel};
+
+fn main() {
+	if let Channel::Nightly = version_meta().unwrap().channel {
+		println!("cargo:rustc-cfg=asm_available");
+	}
+}
diff --git a/tests/src/lib.rs b/tests/src/lib.rs
index 2e0befa..342dbef 100644
--- a/tests/src/lib.rs
+++ b/tests/src/lib.rs
@@ -1,3 +1,5 @@
+#![cfg_attr(asm_available, feature(asm))]
+
 extern crate core;
 #[cfg(test)]
 #[macro_use]
diff --git a/uint/src/lib.rs b/uint/src/lib.rs
index 01d41a7..4a3dc8a 100644
--- a/uint/src/lib.rs
+++ b/uint/src/lib.rs
@@ -8,6 +8,8 @@
 
 //! Efficient large, fixed-size big integers and hashes.
 
+#![cfg_attr(asm_available, feature(asm))]
+
 #[doc(hidden)]
 pub extern crate byteorder;
 
diff --git a/uint/src/uint.rs b/uint/src/uint.rs
index 11da94e..e3260bd 100644
--- a/uint/src/uint.rs
+++ b/uint/src/uint.rs
@@ -77,7 +77,6 @@ macro_rules! uint_overflowing_add_reg {
 #[macro_export]
 #[doc(hidden)]
 macro_rules! uint_overflowing_add {
-	#![feature(asm)]
 	(U256, $n_words:tt, $self_expr: expr, $other: expr) => ({
 		let mut result: [u64; $n_words] = unsafe { ::core::mem::uninitialized() };
 		let self_t: &[u64; $n_words] = &$self_expr.0;
@@ -224,7 +223,6 @@ macro_rules! uint_overflowing_sub_reg {
 #[macro_export]
 #[doc(hidden)]
 macro_rules! uint_overflowing_sub {
-	#![feature(asm)]
 	(U256, $n_words:tt, $self_expr: expr, $other: expr) => ({
 		let mut result: [u64; $n_words] = unsafe { ::core::mem::uninitialized() };
 		let self_t: &[u64; $n_words] = &$self_expr.0;
@@ -300,7 +298,6 @@ macro_rules! uint_overflowing_sub {
 #[cfg(all(asm_available, target_arch="x86_64"))]
 #[macro_export]
 macro_rules! uint_overflowing_mul {
-	#![feature(asm)]
 	(U256, $n_words: expr, $self_expr: expr, $other: expr) => ({
 		let mut result: [u64; $n_words] = unsafe { ::core::mem::uninitialized() };
 		let self_t: &[u64; $n_words] = &$self_expr.0;