diff --git a/ethbloom/Cargo.toml b/ethbloom/Cargo.toml
index 4d8b01d..8c525bf 100644
--- a/ethbloom/Cargo.toml
+++ b/ethbloom/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "ethbloom"
-version = "0.4.0"
+version = "0.4.1"
 authors = ["Parity Technologies <admin@parity.io>"]
 description = "Ethereum bloom filter"
 license = "MIT"
diff --git a/ethbloom/src/lib.rs b/ethbloom/src/lib.rs
index 6fb99e3..6150da8 100644
--- a/ethbloom/src/lib.rs
+++ b/ethbloom/src/lib.rs
@@ -28,8 +28,6 @@
 
 #![cfg_attr(not(feature="std"), no_std)]
 
-#![cfg_attr(asm_available, feature(asm))]
-
 #[cfg(feature="std")]
 extern crate core;
 
diff --git a/ethereum-types/Cargo.toml b/ethereum-types/Cargo.toml
index 33ea15d..f5c7dcd 100644
--- a/ethereum-types/Cargo.toml
+++ b/ethereum-types/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "ethereum-types"
-version = "0.2.0"
+version = "0.2.1"
 authors = ["Parity Technologies <admin@parity.io>"]
 license = "MIT"
 homepage = "https://github.com/paritytech/primitives"
@@ -22,3 +22,4 @@ default = ["std", "heapsizeof", "serialize"]
 std = ["uint/std", "fixed-hash/std", "ethbloom/std"]
 heapsizeof = ["uint/heapsizeof", "fixed-hash/heapsizeof", "ethbloom/heapsizeof"]
 serialize = ["std", "ethereum-types-serialize", "serde", "ethbloom/serialize"]
+use_asm = ["uint/use_asm"]
\ No newline at end of file
diff --git a/ethereum-types/build.rs b/ethereum-types/build.rs
index 432acc3..3ba1687 100644
--- a/ethereum-types/build.rs
+++ b/ethereum-types/build.rs
@@ -11,7 +11,9 @@ 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");
+	if cfg!(feature = "use_asm") { 
+		if let Channel::Nightly = version_meta().unwrap().channel {
+			println!("cargo:rustc-cfg=asm_available");
+		}
 	}
 }
diff --git a/tests/Cargo.toml b/tests/Cargo.toml
index e7b2b21..e466302 100644
--- a/tests/Cargo.toml
+++ b/tests/Cargo.toml
@@ -11,3 +11,6 @@ crunchy = "0.1.5"
 ethereum-types = { path ="../ethereum-types", features = ["std", "heapsizeof"] }
 quickcheck = "0.6"
 uint = { path = "../uint" }
+
+[features]
+use_asm = ["uint/use_asm", "ethereum-types/use_asm"]
\ No newline at end of file
diff --git a/tests/build.rs b/tests/build.rs
index 432acc3..3ba1687 100644
--- a/tests/build.rs
+++ b/tests/build.rs
@@ -11,7 +11,9 @@ 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");
+	if cfg!(feature = "use_asm") { 
+		if let Channel::Nightly = version_meta().unwrap().channel {
+			println!("cargo:rustc-cfg=asm_available");
+		}
 	}
 }
diff --git a/uint/Cargo.toml b/uint/Cargo.toml
index c37a00c..8433f2a 100644
--- a/uint/Cargo.toml
+++ b/uint/Cargo.toml
@@ -4,7 +4,7 @@ homepage = "http://parity.io"
 repository = "https://github.com/paritytech/primitives"
 license = "MIT/Apache-2.0"
 name = "uint"
-version = "0.1.0"
+version = "0.1.1"
 authors = ["Parity Technologies <admin@parity.io>"]
 build = "build.rs"
 
@@ -22,6 +22,7 @@ crunchy = "0.1.5"
 [features]
 std = ["rustc-hex"]
 heapsizeof = ["heapsize"]
+use_asm = []
 
 [[example]]
 name = "modular"
diff --git a/uint/build.rs b/uint/build.rs
index 432acc3..3ba1687 100644
--- a/uint/build.rs
+++ b/uint/build.rs
@@ -11,7 +11,9 @@ 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");
+	if cfg!(feature = "use_asm") { 
+		if let Channel::Nightly = version_meta().unwrap().channel {
+			println!("cargo:rustc-cfg=asm_available");
+		}
 	}
 }