diff --git a/app/models/doi/indexer/related_doi_indexer.rb b/app/models/doi/indexer/related_doi_indexer.rb
index eb97419d3..e81c049f7 100644
--- a/app/models/doi/indexer/related_doi_indexer.rb
+++ b/app/models/doi/indexer/related_doi_indexer.rb
@@ -3,12 +3,12 @@
 module Doi::Indexer
   class RelatedDoiIndexer
     def initialize(related_identifiers)
-      @related_identifiers = related_identifiers
+      @related_identifiers = Array.wrap(related_identifiers)
       @related_dois = nil
     end
 
     def related_dois
-      @related_dois ||= @related_identifiers.select { |r| r["relatedIdentifierType"] == "DOI" }
+      @related_dois ||= @related_identifiers.select { |r| r.fetch("relatedIdentifierType", nil) == "DOI" }
     end
 
     def related_grouped_by_id