diff --git a/StructureDefinition/NHSEngland-DiagnosticReport-GenomicReport.json b/StructureDefinition/NHSEngland-DiagnosticReport-GenomicReport.json
index abcc4ca..be3df23 100644
--- a/StructureDefinition/NHSEngland-DiagnosticReport-GenomicReport.json
+++ b/StructureDefinition/NHSEngland-DiagnosticReport-GenomicReport.json
@@ -165,6 +165,7 @@
         "id": "DiagnosticReport.basedOn",
         "path": "DiagnosticReport.basedOn",
         "definition": "SHOULD reference the originating ServiceRequest if this is an instance of a genomic diagnostic report resulting from a GMS test order.",
+        "max": "1",
         "type": [
           {
             "code": "Reference",