diff --git a/python/lammps/pylammps.py b/python/lammps/pylammps.py
index c693b7d565..05d6d577b9 100644
--- a/python/lammps/pylammps.py
+++ b/python/lammps/pylammps.py
@@ -196,7 +196,7 @@ class Atom(object):
 
     :type: float
     """
-    return self.get("mass", self.index)
+    return self.get("mass", self.type)
 
   @property
   def radius(self):