diff --git a/src/custom-expressions.ts b/src/custom-expressions.ts
index aad8e9d3..5dad438a 100644
--- a/src/custom-expressions.ts
+++ b/src/custom-expressions.ts
@@ -79,5 +79,5 @@ export async function getIdentifier(patient, identifierType) {
   const identifierValue = patient?.identifier?.find(
     (e) => e.id === identifierType
   );
-  return identifierValue.value;
+  return identifierValue?.value;
 }