diff --git a/manifest.yaml b/manifest.yaml
index 484d1b7..64bc911 100644
--- a/manifest.yaml
+++ b/manifest.yaml
@@ -11,8 +11,8 @@ dublin_core:
     description: ""
     format: text/markdown
     identifier: tq
-    issued: 2020-10-05
-    modified: 2020-10-05
+    issued: '2020-10-05'
+    modified: '2020-10-05'
     language:
         direction: ltr
         identifier: th