diff --git a/Cargo.toml b/Cargo.toml
index 28868a5..32811d8 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -20,7 +20,7 @@ doctest = false
 [dependencies]
 
 [features]
-default = ["blake2", "sha1", "sha2", "sha3", "ripemd160", "chacha", "salsa", "hkdf", "hmac", "pbkdf2", "poly1305", "scrypt", "curve25519", "ed25519", "x25519"]
+default = ["std", "blake2", "sha1", "sha2", "sha3", "ripemd160", "chacha", "salsa", "hkdf", "hmac", "pbkdf2", "poly1305", "scrypt", "curve25519", "ed25519", "x25519"]
 blake2 = ["digest", "mac"]
 sha1 = ["digest"]
 sha2 = ["digest"]
@@ -45,3 +45,4 @@ x25519 = ["curve25519"]
 with-bench = []
 force-32bits = []
 use-stdsimd = []
+std = []
diff --git a/src/hashing/blake2/mod.rs b/src/hashing/blake2/mod.rs
index 0e3f350..6f30d12 100644
--- a/src/hashing/blake2/mod.rs
+++ b/src/hashing/blake2/mod.rs
@@ -9,12 +9,24 @@ mod reference;
 
 pub use common::LastBlock;
 
-#[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
+#[cfg(all(
+    any(target_arch = "x86", target_arch = "x86_64"),
+    target_feature = "avx"
+))]
 mod avx;
 
-#[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
+#[cfg(all(
+    any(target_arch = "x86", target_arch = "x86_64"),
+    target_feature = "avx2"
+))]
 mod avx2;
 
+#[cfg(all(
+    any(target_arch = "x86", target_arch = "x86_64"),
+    any(target_feature = "avx", target_feature = "avx2")
+))]
+use crate::simd_check::*;
+
 use common::{b, s};
 
 /// Blake2s Context
@@ -55,11 +67,7 @@ impl EngineS {
         #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
         {
             #[cfg(target_feature = "avx")]
-            const HAS_AVX: bool = true;
-            #[cfg(not(target_feature = "avx"))]
-            const HAS_AVX: bool = false;
-
-            if HAS_AVX {
+            if avx_available() {
                 return avx::compress_s(&mut self.h, &mut self.t, buf, last);
             }
         }
@@ -105,20 +113,13 @@ impl EngineB {
     pub fn compress(&mut self, buf: &[u8], last: LastBlock) {
         #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
         {
-            #[cfg(target_feature = "avx")]
-            const HAS_AVX: bool = true;
-            #[cfg(not(target_feature = "avx"))]
-            const HAS_AVX: bool = false;
-
             #[cfg(target_feature = "avx2")]
-            const HAS_AVX2: bool = true;
-            #[cfg(not(target_feature = "avx2"))]
-            const HAS_AVX2: bool = false;
-
-            if HAS_AVX2 {
+            if avx2_available() {
                 return avx2::compress_b(&mut self.h, &mut self.t, buf, last);
             }
-            if HAS_AVX {
+
+            #[cfg(target_feature = "avx")]
+            if avx_available() {
                 return avx::compress_b(&mut self.h, &mut self.t, buf, last);
             }
         }
diff --git a/src/hashing/sha2/impl256/mod.rs b/src/hashing/sha2/impl256/mod.rs
index 30365ab..82d8f29 100644
--- a/src/hashing/sha2/impl256/mod.rs
+++ b/src/hashing/sha2/impl256/mod.rs
@@ -10,38 +10,45 @@
 
 #[cfg(all(target_arch = "aarch64", feature = "use-stdsimd"))]
 mod aarch64;
-#[cfg(any(target_arch = "x86_64", target_arch = "x86"))]
+
+#[cfg(all(
+    any(target_arch = "x86", target_arch = "x86_64"),
+    target_feature = "avx"
+))]
 mod avx;
-#[cfg(any(target_arch = "x86_64", target_arch = "x86"))]
+
+#[cfg(all(
+    any(target_arch = "x86", target_arch = "x86_64"),
+    target_feature = "sse4.1"
+))]
 mod sse41;
 //TODO not finished yet
 //#[cfg(all(target_arch = "x86_64", target_feature = "sha"))]
 //mod x64sha;
 
+#[cfg(all(
+    any(target_arch = "x86", target_arch = "x86_64"),
+    any(target_feature = "avx", target_feature = "sse4.1")
+))]
+use crate::simd_check::*;
+
 // software implementation valid for all architectures
 mod reference;
 
 pub(crate) fn digest_block(state: &mut [u32; 8], block: &[u8]) {
     #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
     {
-        /// in waiting for https://github.com/rust-lang/rfcs/pull/2725
         #[cfg(target_feature = "avx")]
-        const HAS_AVX: bool = true;
-        #[cfg(not(target_feature = "avx"))]
-        const HAS_AVX: bool = false;
-
-        #[cfg(target_feature = "sse4.1")]
-        const HAS_SSE41: bool = true;
-        #[cfg(not(target_feature = "sse4.1"))]
-        const HAS_SSE41: bool = false;
-
-        if HAS_AVX {
+        if avx_available() {
             return avx::digest_block(state, block);
         }
-        if HAS_SSE41 {
+
+        #[cfg(target_feature = "sse4.1")]
+        if sse4_1_available() {
             return sse41::digest_block(state, block);
         }
     }
+
     #[cfg(target_arch = "aarch64")]
     {
         #[cfg(feature = "use-stdsimd")]
diff --git a/src/lib.rs b/src/lib.rs
index 70a7a53..e97a3c2 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -32,20 +32,18 @@
 #![allow(clippy::wrong_self_convention)]
 #![allow(clippy::identity_op)]
 #![allow(clippy::many_single_char_names)]
-#![no_std]
 #![cfg_attr(feature = "with-bench", feature(test))]
 #![cfg_attr(feature = "use-stdsimd", feature(stdsimd))]
+#![cfg_attr(not(any(feature = "std", test)), no_std)]
 
 #[cfg(test)]
 #[cfg(feature = "with-bench")]
 extern crate test;
 
-#[cfg(not(feature = "std"))]
+#[cfg(not(any(feature = "std", test)))]
 extern crate alloc;
-
-#[cfg(test)]
-#[macro_use]
-extern crate std;
+#[cfg(any(feature = "std", test))]
+extern crate std as alloc;
 
 #[cfg(feature = "blake2")]
 pub mod blake2b;
@@ -107,5 +105,6 @@ pub mod ripemd160;
 
 mod cryptoutil;
 mod simd;
+mod simd_check;
 
 pub mod constant_time;
diff --git a/src/simd_check.rs b/src/simd_check.rs
new file mode 100644
index 0000000..a7c5acf
--- /dev/null
+++ b/src/simd_check.rs
@@ -0,0 +1,38 @@
+#![allow(unreachable_code)]
+#![allow(dead_code)]
+
+pub fn avx_available() -> bool {
+    #[cfg(any(target_arch = "x86", target_arch = "x86_64"))] {
+        #[cfg(feature = "std")] {
+            return std::is_x86_feature_detected!("avx");
+        }
+        #[cfg(all(not(feature = "std"), target_feature = "avx"))] {
+            return true;
+        }
+    }
+    return false;
+}
+
+pub fn avx2_available() -> bool {
+    #[cfg(any(target_arch = "x86", target_arch = "x86_64"))] {
+        #[cfg(feature = "std")] {
+            return std::is_x86_feature_detected!("avx2");
+        }
+        #[cfg(all(not(feature = "std"), target_feature = "avx2"))] {
+            return true;
+        }
+    }
+    return false;
+}
+
+pub fn sse4_1_available() -> bool {
+    #[cfg(any(target_arch = "x86", target_arch = "x86_64"))] {
+        #[cfg(feature = "std")] {
+            return std::is_x86_feature_detected!("sse4.1");
+        }
+        #[cfg(all(not(feature = "std"), target_feature = "sse4.1"))] {
+            return true;
+        }
+    }
+    return false;
+}
\ No newline at end of file