diff --git a/xbee/backend/base.py b/xbee/backend/base.py
index b44998e..4963212 100644
--- a/xbee/backend/base.py
+++ b/xbee/backend/base.py
@@ -115,6 +115,16 @@ def _build_command(self, cmd, **kwargs):
                 if field['len'] is not None:
                     # Was a default value specified?
                     default_value = field['default']
+
+                    if isinstance(default_value, str):
+                        try:
+                            default_value = stringToBytes(default_value)
+                        except Exception as e:
+                            default_aux = default_value
+                            default_value = b''
+                            for i in range(len(default_aux)):
+                                default_value = default_value+ b'\x00'
+
                     if default_value:
                         # If so, use it
                         data = default_value