diff -r ca32821c5fe9 nml/actions/action0.py
--- a/nml/actions/action0.py	Sat Nov 14 11:35:12 2015 +0100
+++ b/nml/actions/action0.py	Fri Dec 11 19:09:38 2015 +0100
@@ -969,15 +969,16 @@
 def parse_sort_block(feature, vehid_list):
     prop_num = [0x1A, 0x20, 0x1B, 0x1B]
     action_list = []
-    last = vehid_list[0]
-    idx = len(vehid_list) - 1
-    while idx >= 0:
-        cur = vehid_list[idx]
-        prop = Action0Property(prop_num[feature], [last], 3)
-        action_list.append(Action0(feature, cur.value))
-        action_list[-1].prop_list.append(prop)
-        last = cur
-        idx -= 1
+    if len(vehid_list) > 0:
+        last = vehid_list[0]
+        idx = len(vehid_list) - 1
+        while idx >= 0:
+            cur = vehid_list[idx]
+            prop = Action0Property(prop_num[feature], [last], 3)
+            action_list.append(Action0(feature, cur.value))
+            action_list[-1].prop_list.append(prop)
+            last = cur
+            idx -= 1
     return action_list
 
 callback_flag_properties = {