diff --git a/spec/config.json b/spec/config.json
index c162cd0f4b..b45bd582dc 100644
--- a/spec/config.json
+++ b/spec/config.json
@@ -1075,6 +1075,7 @@
                   "title": "Refresh Token Rotation Grace Period",
                   "description": "Configures how long a Refresh Token remains valid after it has been used. The maximum value is one hour.",
                   "default": "0s",
+                  "type": "string",
                   "allOf": [
                     {
                       "$ref": "#/definitions/duration"