diff --git a/src/modules/judge/cache/linkedlist.go b/src/modules/judge/cache/linkedlist.go
index fde1ec55..77773ff9 100644
--- a/src/modules/judge/cache/linkedlist.go
+++ b/src/modules/judge/cache/linkedlist.go
@@ -90,6 +90,12 @@ func (ll *SafeLinkedList) HistoryData(limit int) ([]*dataobj.HistoryData, bool)
 		currentElement := firstElement
 		for i < limit {
 			nextElement := currentElement.Next()
+
+			if nextElement == nil {
+				isEnough = false
+				return vs, isEnough
+			}
+
 			vs[i] = &dataobj.HistoryData{
 				Timestamp: nextElement.Value.(*dataobj.JudgeItem).Timestamp,
 				Value:     dataobj.JsonFloat(nextElement.Value.(*dataobj.JudgeItem).Value),
diff --git a/src/modules/tsdb/rrdtool/rrdtool.go b/src/modules/tsdb/rrdtool/rrdtool.go
index 3f80b207..f6d4d80e 100644
--- a/src/modules/tsdb/rrdtool/rrdtool.go
+++ b/src/modules/tsdb/rrdtool/rrdtool.go
@@ -47,7 +47,7 @@ func update(filename string, items []*dataobj.TsdbItem) error {
 		if v > 1e+300 || (v < 1e-300 && v > 0) {
 			continue
 		}
-		u.Cache(item.Timestamp, int(item.Value))
+		u.Cache(item.Timestamp, item.Value)
 	}
 
 	return u.Update()