diff --git a/api/v1/swagger/definitions/patron.json b/api/v1/swagger/definitions/patron.json
index 90d5c9adf6..9ef6cabebc 100644
--- a/api/v1/swagger/definitions/patron.json
+++ b/api/v1/swagger/definitions/patron.json
@@ -144,6 +144,7 @@
     },
     "date_renewed": {
       "type": ["string", "null"],
+      "format": "date",
       "description": "date the patron's card was last renewed"
     },
     "incorrect_address": {