diff --git a/chacha20_poly1305/src/chacha20.rs b/chacha20_poly1305/src/chacha20.rs
index 34f041304..a93e0f1e6 100644
--- a/chacha20_poly1305/src/chacha20.rs
+++ b/chacha20_poly1305/src/chacha20.rs
@@ -328,11 +328,8 @@ impl ChaCha20 {
         }
     }
 
-    /// Get the keystream block at a specified block.
-    pub fn get_keystream(&mut self, block: u32) -> [u8; 64] {
-        self.block(block);
-        self.keystream_at_block(self.block_count)
-    }
+    /// Get the keystream for specified block.
+    pub fn get_keystream(&self, block: u32) -> [u8; 64] { self.keystream_at_block(block) }
 
     /// Update the index of the keystream to the given byte.
     pub fn seek(&mut self, seek: u32) {
diff --git a/chacha20_poly1305/src/lib.rs b/chacha20_poly1305/src/lib.rs
index 42b2df3af..1627b511e 100644
--- a/chacha20_poly1305/src/lib.rs
+++ b/chacha20_poly1305/src/lib.rs
@@ -118,7 +118,7 @@ impl ChaCha20Poly1305 {
         tag: [u8; 16],
         aad: Option<&[u8]>,
     ) -> Result<(), Error> {
-        let mut chacha = ChaCha20::new_from_block(self.key, self.nonce, 0);
+        let chacha = ChaCha20::new_from_block(self.key, self.nonce, 0);
         let keystream = chacha.get_keystream(0);
         let mut poly =
             Poly1305::new(keystream[..32].try_into().expect("slicing produces 32-byte slice"));