diff --git a/base/tasklist.py b/base/tasklist.py
index 0ffbf51..b16dffc 100644
--- a/base/tasklist.py
+++ b/base/tasklist.py
@@ -38,11 +38,12 @@ class TaskList(object):
 		from common.phases import order
 		graph = {}
 		for task in tasks:
-			graph[task] = []
-			graph[task].extend([self.get(succ) for succ in task.before])
-			graph[task].extend([succ for succ in tasks if type(task) in succ.after])
+			successors = []
+			successors.extend([self.get(succ) for succ in task.before])
+			successors.extend(filter(lambda succ: type(task) in succ.after, tasks))
 			succeeding_phases = order[order.index(task.phase)+1:]
-			graph[task].extend([succ for succ in tasks if succ.phase in succeeding_phases])
+			successors.extend(filter(lambda succ: succ.phase in succeeding_phases, tasks))
+			graph[task] = filter(lambda succ: succ in self.tasks, successors)
 
 		components = self.strongly_connected_components(graph)
 		cycles_found = 0