diff --git a/lib/kiss/kiss_serial.rb b/lib/kiss/kiss_serial.rb
index 39e1a5512fb6f25d4b2cd1768220ccbd21bb3930..4a3e44c659f00089b51a98e7e6794af89cb4fdb8 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 }.join
+            data.map { |b| b.chr }.to_s
             puts 'write_interface:'
             p data
             @serial.write(data)