diff --git a/go/master/service.go b/go/master/service.go
index b1334a2d8e6c943daa2e0f5df203442beb9af107..daf39282302420298cc4cd06e4133a34aabc4776 100644
--- a/go/master/service.go
+++ b/go/master/service.go
@@ -414,7 +414,7 @@ func (s *Service) TaskFailed(taskID TaskID, dummy *int) error {
 	t, ok := s.taskQueues.Pending[taskID.ID]
 	if !ok {
 		err := errors.New("pending task not found")
-		log.WithFields(s.logFields()).Warningln("TaskFailed:Pending task #%d not found.", taskID)
+		log.WithFields(s.logFields()).Warningln("TaskFailed:Pending task #%v not found.", taskID)
 		return err
 	}