diff --git a/src/lib.rs b/src/lib.rs
index dc27629..fbe8087 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -8,6 +8,8 @@
 //! [`sapling-crypto`]: https://crates.io/crates/sapling-crypto
 //! [`orchard`]: https://crates.io/crates/orchard
 
+#![no_std]
+#![deny(unsafe_code)]
 #![deny(rustdoc::broken_intra_doc_links)]
 
 mod prf_expand;
diff --git a/src/prf_expand.rs b/src/prf_expand.rs
index 28537e7..212c841 100644
--- a/src/prf_expand.rs
+++ b/src/prf_expand.rs
@@ -1,4 +1,4 @@
-use std::marker::PhantomData;
+use core::marker::PhantomData;
 
 use blake2b_simd::Params;