diff --git a/src/ed25519.rs b/src/ed25519.rs
index 919ecb4..e25003d 100644
--- a/src/ed25519.rs
+++ b/src/ed25519.rs
@@ -173,6 +173,13 @@ impl Debug for SecretKey {
     }
 }
 
+/// Overwrite secret key material with null bytes when it goes out of scope.
+impl Drop for SecretKey {
+    fn drop(&mut self) {
+        self.0 = [0u8; SECRET_KEY_LENGTH];
+    }
+}
+
 impl SecretKey {
     /// Expand this `SecretKey` into an `ExpandedSecretKey`.
     pub fn expand<D>(&self) -> ExpandedSecretKey where D: Digest<OutputSize = U64> + Default {
@@ -375,6 +382,14 @@ pub struct ExpandedSecretKey {
     pub (crate) nonce: [u8; 32],
 }
 
+/// Overwrite secret key material with null bytes when it goes out of scope.
+impl Drop for ExpandedSecretKey {
+    fn drop(&mut self) {
+        self.key = Scalar::zero();
+        self.nonce = [0u8; 32];
+    }
+}
+
 #[cfg(feature = "sha2")]
 impl<'a> From<&'a SecretKey> for ExpandedSecretKey {
     /// Construct an `ExpandedSecretKey` from a `SecretKey`.