diff --git a/xray/utils.py b/xray/utils.py
index df74ab5..1fcf2b6 100644
--- a/xray/utils.py
+++ b/xray/utils.py
@@ -290,7 +290,7 @@ def attenuation_length(compound, density=None, natural_density=None,energy=None,
 
 def transmission(material='Si',thickness=100e-6, density=None, natural_density=None,energy=None, wavelength=None):
   """ extend periodictable.xsf capabilities """
-  att_len = attenuation_length(compound,density=density,
+  att_len = attenuation_length(material,density=density,
             natural_density=natural_density,energy=energy,wavelength=wavelength)
   return np.exp(-thickness/att_len)