diff --git a/api/arrange.py b/api/arrange.py
index ac5520f..627880a 100644
--- a/api/arrange.py
+++ b/api/arrange.py
@@ -29,7 +29,7 @@ def topo_sort(graph):
 
     column_index = {}
     for node in reversed(sorted_nodes):
-        column_index[node] = max([ column_index[node] for node in graph[node] ], default=-1) + 1
+        column_index[node] = max([ column_index[adj_node] for adj_node in graph[node] ], default=-1) + 1
         if column_index[node] == len(columns):
             columns.append([node])
         else: