diff --git a/hashes/src/lib.rs b/hashes/src/lib.rs
index 00ca7fd70..cc5d191bc 100644
--- a/hashes/src/lib.rs
+++ b/hashes/src/lib.rs
@@ -50,7 +50,7 @@
 //! # }
 //! ```
 
-#![cfg_attr(not(feature = "std"), no_std)]
+#![no_std]
 // Experimental features we need.
 #![cfg_attr(docsrs, feature(doc_auto_cfg))]
 #![cfg_attr(bench, feature(test))]
@@ -70,6 +70,9 @@ extern crate alloc;
 
 extern crate core;
 
+#[cfg(feature = "std")]
+extern crate std;
+
 #[cfg(feature = "bitcoin-io")]
 extern crate bitcoin_io as io;
 
diff --git a/hashes/src/sha256.rs b/hashes/src/sha256.rs
index 6cdad22c9..42fe5cf24 100644
--- a/hashes/src/sha256.rs
+++ b/hashes/src/sha256.rs
@@ -491,10 +491,10 @@ impl HashEngine {
     fn process_block(&mut self) {
         #[cfg(all(feature = "std", any(target_arch = "x86", target_arch = "x86_64")))]
         {
-            if is_x86_feature_detected!("sse4.1")
-                && is_x86_feature_detected!("sha")
-                && is_x86_feature_detected!("sse2")
-                && is_x86_feature_detected!("ssse3")
+            if std::is_x86_feature_detected!("sse4.1")
+                && std::is_x86_feature_detected!("sha")
+                && std::is_x86_feature_detected!("sse2")
+                && std::is_x86_feature_detected!("ssse3")
             {
                 return unsafe { self.process_block_simd_x86_intrinsics() };
             }