diff --git a/src/sodium/cipher/aead/chalsa.cr b/src/sodium/cipher/aead/chalsa.cr
index 92bd1bf..f9d20ff 100644
--- a/src/sodium/cipher/aead/chalsa.cr
+++ b/src/sodium/cipher/aead/chalsa.cr
@@ -78,8 +78,9 @@ module Sodium::Cipher::Aead
 
     abstract def encrypt_detached(src : Bytes, dst : Bytes? = nil, *, nonce : Sodium::Nonce? = nil, mac : Bytes? = nil, additional : String | Bytes | Nil = nil) : {Bytes, Bytes, Sodium::Nonce}
     abstract def decrypt_detached(src : Bytes, dst : Bytes? = nil, *, nonce : Sodium::Nonce, mac : Bytes, additional : String | Bytes | Nil = nil) : Bytes
-    protected abstract def key_size : Int32
-    protected abstract def mac_size : Int32
+    abstract def key_size : Int32
+    abstract def mac_size : Int32
+    abstract def nonce_size : Int32
 
     def dup
       self.class.new @key.dup
@@ -143,13 +144,17 @@ module Sodium::Cipher::Aead
         dst
       end
 
-      protected def key_size : Int32
+      def key_size : Int32
         KEY_SIZE
       end
 
-      protected def mac_size : Int32
+      def mac_size : Int32
         MAC_SIZE
       end
+
+      def nonce_size : Int32
+        NONCE_SIZE
+      end
     end
   {% end %}
 end