diff --git a/lib/jekyll/pdf/generator.rb b/lib/jekyll/pdf/generator.rb
index db712c6..2acc3ae 100644
--- a/lib/jekyll/pdf/generator.rb
+++ b/lib/jekyll/pdf/generator.rb
@@ -6,7 +6,7 @@ module Jekyll
 
       def generate(site)
         # Loop through pages & documents and build PDFs
-        [site.pages, site.documents].each do |items|
+        [site.pages.clone, site.documents].each do |items|
           items.each do |item|
             site.pages << Document.new(site, site.source, item) if item.data['pdf']
           end