diff --git a/lib/iiif_manifest/manifest_builder/structure_builder.rb b/lib/iiif_manifest/manifest_builder/structure_builder.rb
index a3929cc..5728e9c 100644
--- a/lib/iiif_manifest/manifest_builder/structure_builder.rb
+++ b/lib/iiif_manifest/manifest_builder/structure_builder.rb
@@ -51,7 +51,7 @@ def build_range
 
       def sub_ranges
         @sub_ranges ||= record.ranges.each_with_index.map do |sub_range, child_index|
-          RangeBuilder.new(sub_range, parent, child_index + (index + 1))
+          RangeBuilder.new(sub_range, parent, child_index + (index + record.ranges.length))
         end
       end