diff --git a/sha1-checked/src/lib.rs b/sha1-checked/src/lib.rs
index c5475bca..25baf66e 100644
--- a/sha1-checked/src/lib.rs
+++ b/sha1-checked/src/lib.rs
@@ -23,6 +23,9 @@ pub use digest::{self, Digest};
 
 use core::slice::from_ref;
 
+#[cfg(feature = "std")]
+extern crate std;
+
 #[cfg(feature = "zeroize")]
 use digest::zeroize::{Zeroize, ZeroizeOnDrop};
 use digest::{