diff --git a/api/v1/swagger/definitions/patron.json b/api/v1/swagger/definitions/patron.json
index a021502f8e4..84f298ae134 100644
--- a/api/v1/swagger/definitions/patron.json
+++ b/api/v1/swagger/definitions/patron.json
@@ -269,6 +269,10 @@
     "updated_on": {
       "type": "string",
       "description": "time of last change could be useful for synchronization with external systems (among others)"
+    },
+    "lastseen": {
+      "type": ["string", "null"],
+      "description": "last time a patron has been seen (connected at the OPAC or staff interface)"
     }
   }
 }