diff --git a/lib/ably/util/crypto.rb b/lib/ably/util/crypto.rb
index 3635b59a5..7707af93e 100644
--- a/lib/ably/util/crypto.rb
+++ b/lib/ably/util/crypto.rb
@@ -83,8 +83,8 @@ def encrypt(payload, encrypt_options = {})
       cipher.key = key
       iv = encrypt_options[:iv] || fixed_iv || cipher.random_iv
       cipher.iv = iv
-
-      iv << cipher.update(payload) << cipher.final
+      iv << cipher.update(payload) unless payload.empty?
+      iv << cipher.final
     end
 
     # Decrypt payload using configured Cipher