diff --git a/urdf_parser_py/src/urdf_parser_py/urdf.py b/urdf_parser_py/src/urdf_parser_py/urdf.py
index 504d1a79..2832a65e 100644
--- a/urdf_parser_py/src/urdf_parser_py/urdf.py
+++ b/urdf_parser_py/src/urdf_parser_py/urdf.py
@@ -224,8 +224,8 @@ def __init__(self, rising=None, falling=None):
 		self.falling = falling
 
 xmlr.reflect(JointCalibration, params = [
-	xmlr.Attribute('rising', float),
-	xmlr.Attribute('falling', float)
+	xmlr.Attribute('rising', float, False),
+	xmlr.Attribute('falling', float, False)
 	])
 
 class JointLimit(xmlr.Object):
@@ -339,10 +339,10 @@ def __init__(self, name = None, joint = None, actuator = None, type = None, mech
 
 xmlr.reflect(PR2Transmission, tag = 'pr2_transmission', params = [
 	name_attribute,
-	xmlr.Attribute('type', str),
-	xmlr.Element('joint', 'element_name'),
-	xmlr.Element('actuator', 'element_name'),
-	xmlr.Element('mechanicalReduction', float)
+	xmlr.Attribute('type', str, False),
+	xmlr.Element('joint', 'element_name', False),
+	xmlr.Element('actuator', 'element_name', False),
+	xmlr.Element('mechanicalReduction', float, False)
 	])