diff --git a/src/scripts/validate-sgid-index.mjs b/src/scripts/validate-sgid-index.mjs
index e2ebe6b5d..c74a71f66 100644
--- a/src/scripts/validate-sgid-index.mjs
+++ b/src/scripts/validate-sgid-index.mjs
@@ -136,7 +136,7 @@ async function duplicates(row) {
       continue;
     }
 
-    if (duplicateLookups[field][value].length > 1) {
+    if (duplicateLookups[field][value]?.length > 1) {
       recordError(`duplicate ${field}: "${value}" found`, row);
     }
   }