diff --git a/Cargo.toml b/Cargo.toml
index 98dd770..e5af2f7 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -36,6 +36,7 @@ version = "^0.6"
 
 [dev-dependencies]
 rustc-serialize = "0.3"
+blake2 = "^0.4"
 
 [features]
 default = ["std"]
diff --git a/src/ed25519.rs b/src/ed25519.rs
index 74863c6..87d38d7 100644
--- a/src/ed25519.rs
+++ b/src/ed25519.rs
@@ -497,8 +497,6 @@ mod test {
 mod bench {
     use blake2::Blake2b;
     use digest::Digest;
-    use generic_array::GenericArray;
-    use generic_array::typenum::{U64, U128};
     use test::Bencher;
     use rand::OsRng;
     use super::*;
@@ -522,27 +520,6 @@ mod bench {
         }
     }
 
-    /// A fake hash function which simply returns zeroes.
-    struct ZeroDigest;
-
-    impl ZeroDigest {
-        pub fn new() -> ZeroDigest {
-            ZeroDigest
-        }
-    }
-
-    impl Digest for ZeroDigest {
-        type OutputSize = U64;
-        type BlockSize = U128;
-
-        fn input(&mut self, _input: &[u8]) { }
-        fn result(self) -> GenericArray<u8, Self::OutputSize> { GenericArray::default() }
-    }
-
-    impl Default for ZeroDigest {
-        fn default() -> Self { Self::new() }
-    }
-
     #[bench]
     fn sign(b: &mut Bencher) {
         let mut cspring: OsRng = OsRng::new().unwrap();