diff --git a/.github/workflows/rust.yaml b/.github/workflows/rust.yaml
index bc09afc..da26cf4 100644
--- a/.github/workflows/rust.yaml
+++ b/.github/workflows/rust.yaml
@@ -6,6 +6,9 @@ jobs:
   run:
     name: Run
     runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        features: [--all-features, --no-default-features]
     steps:
       - name: Install Rust stable
         uses: actions-rs/toolchain@v1
@@ -22,16 +25,16 @@ jobs:
         uses: actions-rs/cargo@v1
         with:
           command: build
-          args: --workspace
+          args: --workspace ${{ matrix.features }}
 
       - name: Lint
         uses: actions-rs/cargo@v1
         with:
           command: clippy
-          args: --workspace -- -D warnings
+          args: --workspace ${{ matrix.features }} -- -D warnings
 
       - name: Test
         uses: actions-rs/cargo@v1
         with:
           command: test
-          args: --workspace
+          args: --workspace ${{ matrix.features }}
diff --git a/Cargo.toml b/Cargo.toml
index 7fcefd9..edd76eb 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -9,11 +9,15 @@ repository = "https://github.com/mlafeldt/codebreaker-rs"
 documentation = "https://docs.rs/codebreaker/"
 homepage = "https://crates.io/crates/codebreaker"
 keywords = ["codebreaker", "ps2", "gamehacking", "homebrew"]
-categories = ["algorithms", "cryptography"]
+categories = ["algorithms", "cryptography", "no-std"]
 edition = "2018"
 
 [lib]
 name = "codebreaker"
 
 [dependencies]
-num-bigint = "^0.2.4"
+num-bigint = "0.3"
+
+[features]
+default = ["std"]
+std = ["num-bigint/std"]
diff --git a/src/cb1.rs b/src/cb1.rs
index cd2794d..7dcf243 100644
--- a/src/cb1.rs
+++ b/src/cb1.rs
@@ -98,6 +98,7 @@ const SEEDS: [[u32; 16]; 3] = [
 mod tests {
     use super::*;
     use crate::code;
+    use crate::std_alloc::Vec;
 
     struct Test {
         decrypted: &'static str,
diff --git a/src/cb7.rs b/src/cb7.rs
index 1621972..36c888f 100644
--- a/src/cb7.rs
+++ b/src/cb7.rs
@@ -1,10 +1,11 @@
 //! Encrypt and decrypt cheat codes for CodeBreaker PS2 v7+.
 
 use crate::rc4::Rc4;
+use crate::std_alloc::Vec;
 
-use std::fmt;
-use std::mem::size_of;
-use std::slice;
+use core::fmt;
+use core::mem::size_of;
+use core::slice;
 
 /// A processor for CB v7+ codes.
 #[derive(Clone, Copy)]
@@ -466,6 +467,7 @@ const SEEDS: [[u8; 256]; 5] = [
 mod tests {
     use super::*;
     use crate::code;
+    use crate::std_alloc::Vec;
 
     fn mul_tests() -> Vec<(u32, u32, u32)> {
         vec![
diff --git a/src/lib.rs b/src/lib.rs
index 619915a..05f0951 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -30,6 +30,30 @@
 #![deny(clippy::all, clippy::nursery)]
 #![deny(nonstandard_style, rust_2018_idioms)]
 #![deny(missing_docs, missing_debug_implementations)]
+#![no_std]
+
+#[cfg(feature = "std")]
+#[macro_use]
+extern crate std;
+
+#[cfg(feature = "std")]
+mod std_alloc {
+    #[cfg(test)]
+    pub use std::string::String;
+    pub use std::vec::Vec;
+}
+
+#[cfg(not(feature = "std"))]
+#[allow(unused_imports)]
+#[macro_use]
+extern crate alloc;
+
+#[cfg(not(feature = "std"))]
+mod std_alloc {
+    #[cfg(test)]
+    pub use alloc::string::String;
+    pub use alloc::vec::Vec;
+}
 
 pub mod cb1;
 pub mod cb7;
@@ -286,6 +310,7 @@ fn num_code_lines(addr: u32) -> usize {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::std_alloc::Vec;
 
     struct Test {
         cb: Codebreaker,
@@ -491,7 +516,9 @@ mod tests {
 
 #[cfg(test)]
 mod code {
-    pub(crate) fn parse(line: &str) -> (u32, u32) {
+    use crate::std_alloc::{String, Vec};
+
+    pub fn parse(line: &str) -> (u32, u32) {
         let code: Vec<u32> = line
             .splitn(2, ' ')
             .map(|v| u32::from_str_radix(v, 16).unwrap())
@@ -499,7 +526,7 @@ mod code {
         (code[0], code[1])
     }
 
-    pub(crate) fn format(code: (u32, u32)) -> String {
+    pub fn format(code: (u32, u32)) -> String {
         format!("{:08X} {:08X}", code.0, code.1)
     }
 }
diff --git a/src/rc4.rs b/src/rc4.rs
index 09bb8e7..15fd827 100644
--- a/src/rc4.rs
+++ b/src/rc4.rs
@@ -38,6 +38,7 @@ impl Rc4 {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::std_alloc::Vec;
 
     struct Test {
         key: &'static str,