diff --git a/hdr_schemata/models/GWDM/1.1/schema.json b/hdr_schemata/models/GWDM/1.1/schema.json
index ed5f3de..823bf56 100644
--- a/hdr_schemata/models/GWDM/1.1/schema.json
+++ b/hdr_schemata/models/GWDM/1.1/schema.json
@@ -1344,6 +1344,7 @@
                                           "type": "null"
                                     }
                               ],
+                              "default": null,
                               "description": "Summary population size of the cohort",
                               "title": "Population size"
                         }
@@ -1358,8 +1359,7 @@
                         "contactPoint",
                         "datasetType",
                         "description",
-                        "publisher",
-                        "populationSize"
+                        "publisher"
                   ],
                   "title": "Summary",
                   "type": "object"
diff --git a/hdr_schemata/models/GWDM/v1_1/Summary.py b/hdr_schemata/models/GWDM/v1_1/Summary.py
index 6e686a4..f617155 100644
--- a/hdr_schemata/models/GWDM/v1_1/Summary.py
+++ b/hdr_schemata/models/GWDM/v1_1/Summary.py
@@ -14,7 +14,7 @@ class Summary(BaseSummary):
 
     # new field for a summary of the population size
     populationSize: Optional[int] = Field(
-        ...,
+        None,
         description="Summary population size of the cohort",
         title="Population size",
     )