diff --git a/structuredefinitions/UKCore-DiagnosticReport.xml b/structuredefinitions/UKCore-DiagnosticReport.xml
index 718f7e17..794bd376 100644
--- a/structuredefinitions/UKCore-DiagnosticReport.xml
+++ b/structuredefinitions/UKCore-DiagnosticReport.xml
@@ -34,9 +34,9 @@
         <severity value="error" />
         <human value="Only one of DiagnosticReport.media.link or DiagnosticReport.media.extension:mediaLinkR5 can be populated at a time." />
         <expression
-          value="( (media.link.exists() and not extension(http://hl7.org/fhir/5.0/StructureDefinition/extension-DiagnosticReport.media.link
+          value="(media.link.exists() and not extension('http://hl7.org/fhir/5.0/StructureDefinition/extension-DiagnosticReport.media.link'
 ).exists()) or (not media.link.exists() and extension('http://hl7.org/fhir/5.0/StructureDefinition/extension-DiagnosticReport.media.link
-').exists()) )
+').exists()) 
 " />
       </constraint>
     </element>