diff --git a/src/lib.rs b/src/lib.rs
index f59af63..751eb24 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -21,15 +21,23 @@
     unsafe_code
 )]
 #![warn(rust_2018_idioms)]
+#![no_std]
+
+extern crate alloc;
+
+#[cfg(test)]
+extern crate std;
 
 mod u256;
 
-use std::{
+use alloc::{
     collections::{BTreeMap, BTreeSet, VecDeque},
-    ops::RangeFrom,
+    vec,
+    vec::Vec,
 };
+use core::ops::RangeFrom;
 
-use u256::U256;
+use self::u256::U256;
 
 #[derive(Debug, Clone)]
 #[repr(transparent)]
diff --git a/src/u256.rs b/src/u256.rs
index bfee984..48b76d6 100644
--- a/src/u256.rs
+++ b/src/u256.rs
@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-use std::{
+use core::{
     cmp::Ordering,
     ops::{
         Add, AddAssign, BitAnd, BitOrAssign, Shl, ShlAssign, Sub, SubAssign,