diff --git a/api/coreservice.go b/api/coreservice.go
index 3fbfd3ad85..d83bf4f79d 100644
--- a/api/coreservice.go
+++ b/api/coreservice.go
@@ -1318,10 +1318,9 @@ func (core *coreService) reverseActionsInBlock(blk *block.Block, reverseStart, c
 	if reverseStart > size || count == 0 {
 		return nil
 	}
-	// TODO (saito): fix overflow
-	start := size - (reverseStart + count)
-	if start < 0 {
-		start = 0
+	start := uint64(0)
+	if size > reverseStart+count {
+		start = size - (reverseStart + count)
 	}
 	end := size - 1 - reverseStart
 	res := make([]*iotexapi.ActionInfo, 0, start-end+1)