diff --git a/tools/sched/schedgraph.py b/tools/sched/schedgraph.py
index 4335574972e..e5925141e69 100644
--- a/tools/sched/schedgraph.py
+++ b/tools/sched/schedgraph.py
@@ -856,7 +856,7 @@ class EventSource:
 		return (Y_EVENTSOURCE)
 
 	def eventat(self, i):
-		if (i >= len(self.events)):
+		if (i >= len(self.events) or i < 0):
 			return (None)
 		event = self.events[i]
 		return (event)