diff --git a/src/Controller/RelatedRorController.php b/src/Controller/RelatedRorController.php
index a67d39e..d925fad 100644
--- a/src/Controller/RelatedRorController.php
+++ b/src/Controller/RelatedRorController.php
@@ -117,6 +117,10 @@ class RelatedRorController extends ControllerBase {
     }
 
     private function getSimilarity(array $orig, array $other): int {
+        if(!in_array('field_tags', $orig) || count($orig['field_tags']) == 0 || 
+            !in_array('field_tags', $other) || count($other['field_tags']) == 0) {
+            return 0;
+        }
         $orig_tags = array_map(function($t) { return $t['target_id']; }, $orig['field_tags']);
         $other_tags = array_map(function($t) { return $t['target_id']; }, $other['field_tags']);
         $both = array_intersect($orig_tags, $other_tags);