diff --git a/sdk/lib/stellar/client.rb b/sdk/lib/stellar/client.rb
index c62db067..93da8908 100644
--- a/sdk/lib/stellar/client.rb
+++ b/sdk/lib/stellar/client.rb
@@ -199,7 +199,7 @@ def submit_transaction(tx_envelope:, options: {skip_memo_required_check: false})
       unless options[:skip_memo_required_check]
         check_memo_required(tx_envelope)
       end
-      @horizon.transactions._post(tx: Base64.encode64(tx_envelope.to_xdr))
+      @horizon.transactions._post(tx: tx_envelope.to_xdr(:base64))
     end
 
     # Required by SEP-0029