diff --git a/steam/items.py b/steam/items.py
index d25122e..6b0dfc0 100644
--- a/steam/items.py
+++ b/steam/items.py
@@ -652,7 +652,8 @@ def __init__(self, item, schema=None):
 
             if schema:
                 attrdef = schema._attribute_definition(index)
-                index = attrdef["defindex"]
+                if attrdef:
+                    index = attrdef["defindex"]
 
             self._attributes.setdefault(index, {})
 
@@ -666,7 +667,10 @@ def __init__(self, item, schema=None):
                 index = attr["defindex"]
 
                 if schema and index not in self._attributes:
-                    self._attributes[index] = schema._attribute_definition(index)
+                    attrdef = schema._attribute_definition(index)
+
+                    if attrdef:
+                        self._attributes[index] = attrdef
 
                 self._attributes.setdefault(index, {})
                 self._attributes[index].update(attr)