diff --git a/bin/validate-cocina b/bin/validate-cocina
index 14ce6afc1..2bf87ec45 100755
--- a/bin/validate-cocina
+++ b/bin/validate-cocina
@@ -68,7 +68,7 @@ def validate(clazz, sample_size, processes)
     rescue StandardError => e
       [obj.external_identifier, clazz.name, e.message]
     end
-  end.flatten
+  end.flatten(1)
 end
 
 results = validate(Dro, options[:sample],