diff --git a/lib/kiss/kiss_serial.rb b/lib/kiss/kiss_serial.rb
index dc2ffe78cdae3cace9503cee998f4bb9ec5613dc..4883c14ddc855a44ac534fb044429948d8122252 100644
--- a/lib/kiss/kiss_serial.rb
+++ b/lib/kiss/kiss_serial.rb
@@ -41,7 +41,7 @@ module Kiss
 
         protected
         def write_interface(data)
-            data.map { |b| b.chr }.to_s
+            data = data.map { |b| b.chr }.to_s
             puts 'write_interface:'
             p data
             @serial.write(data)