diff --git a/core/rosmaster/src/rosmaster/master_api.py b/core/rosmaster/src/rosmaster/master_api.py
index 2c168471..9a5ce501 100644
--- a/core/rosmaster/src/rosmaster/master_api.py
+++ b/core/rosmaster/src/rosmaster/master_api.py
@@ -148,8 +148,8 @@ def apivalidate(error_return_value, validators=()):
                         try:
                             newArgs.append(v(a, caller_id)) 
                         except ParameterInvalid, e:
-                            _logger.error("%s: invalid parameter: %s", f.func_name, e.message or 'error')
-                            return -1, e.message or 'error', error_return_value
+                            _logger.error("%s: invalid parameter: %s", f.func_name, str(e) or 'error')
+                            return -1, str(e) or 'error', error_return_value
                     else:
                         newArgs.append(a)
 
diff --git a/core/rosmaster/src/rosmaster/validators.py b/core/rosmaster/src/rosmaster/validators.py
index 0dd156a7..62431728 100644
--- a/core/rosmaster/src/rosmaster/validators.py
+++ b/core/rosmaster/src/rosmaster/validators.py
@@ -41,10 +41,10 @@ ROSRPC = "rosrpc://"
 class ParameterInvalid(Exception):
     """Exception that is raised when a parameter fails validation checks"""
     def __init__(self, message):
-        self.message = message
+        self._message = message
 
     def __str__(self):
-        return str(self.message)
+        return str(self._message)
 
 def non_empty(param_name):
     """Validator that checks that parameter is not empty"""