diff --git a/zssp/src/zssp.rs b/zssp/src/zssp.rs
index 536f3c8b7..ab6324f78 100644
--- a/zssp/src/zssp.rs
+++ b/zssp/src/zssp.rs
@@ -130,12 +130,13 @@ enum Offer {
     RekeyInit(P384KeyPair, i64),
 }
 
+const AES_POOL_SIZE: usize = 4;
 struct SessionKey {
-    ratchet_key: Secret<BASE_KEY_SIZE>, // Key used in derivation of the next session key
+    ratchet_key: Secret<BASE_KEY_SIZE>,            // Key used in derivation of the next session key
     //receive_key: Secret<AES_256_KEY_SIZE>,       // Receive side AES-GCM key
     //send_key: Secret<AES_256_KEY_SIZE>,          // Send side AES-GCM key
-    receive_cipher_pool: [Mutex<AesGcm<false>>; 4], // Pool of reusable sending ciphers
-    send_cipher_pool: [Mutex<AesGcm<true>>; 4],     // Pool of reusable receiving ciphers
+    receive_cipher_pool: [Mutex<AesGcm<false>>; AES_POOL_SIZE], // Pool of reusable sending ciphers
+    send_cipher_pool: [Mutex<AesGcm<true>>; AES_POOL_SIZE],     // Pool of reusable receiving ciphers
     rekey_at_time: i64,                             // Rekey at or after this time (ticks)
     created_at_counter: u64,                        // Counter at which session was created
     rekey_at_counter: u64,                          // Rekey at or after this counter
@@ -1575,20 +1576,24 @@ impl SessionKey {
 
     fn get_send_cipher<'a>(&'a self, counter: u64) -> Result<MutexGuard<'a, AesGcm<true>>, Error> {
         if counter < self.expire_at_counter {
-            //for i in 0..self.send_cipher_pool.len() {
-            //    let mutex = &self.send_cipher_pool[(counter as usize + i)%self.send_cipher_pool.len()];
-            //    if let Ok(guard) = mutex.try_lock() {
-            //        return Ok(guard);
-            //    }
-            //}
-            Ok(self.send_cipher_pool[(counter as usize)%self.send_cipher_pool.len()].lock().unwrap())
+            for i in 0..(AES_POOL_SIZE - 1) {
+                if let Ok(p) = self.send_cipher_pool[(counter as usize).wrapping_add(i)%AES_POOL_SIZE].try_lock() {
+                    return Ok(p);
+                }
+            }
+            Ok(self.send_cipher_pool[(counter as usize)%AES_POOL_SIZE].lock().unwrap())
         } else {
             Err(Error::MaxKeyLifetimeExceeded)
         }
     }
 
     fn get_receive_cipher<'a>(&'a self, counter: u64) -> MutexGuard<'a, AesGcm<false>> {
-        self.receive_cipher_pool[(counter as usize)%self.receive_cipher_pool.len()].lock().unwrap()
+        for i in 0..(AES_POOL_SIZE - 1) {
+            if let Ok(p) = self.receive_cipher_pool[(counter as usize).wrapping_add(i)%AES_POOL_SIZE].try_lock() {
+                return p;
+            }
+        }
+        self.receive_cipher_pool[(counter as usize)%AES_POOL_SIZE].lock().unwrap()
     }
 }