diff --git a/lib/jekyll-pandoc-multiple-formats/unite.rb b/lib/jekyll-pandoc-multiple-formats/unite.rb
index 2df3cd33dc7c957943c4d156181bcd6dedb21786..04b08dd039bb5fbaa00796d7121efb6a9bc12ba6 100644
--- a/lib/jekyll-pandoc-multiple-formats/unite.rb
+++ b/lib/jekyll-pandoc-multiple-formats/unite.rb
@@ -40,18 +40,19 @@ module JekyllPandocMultipleFormats
       raise ArgumentError.new 'An array of filenames is required' unless files.is_a? Array
 
       @output_file = output_file
-      @files       = files
+      self.files   = files
 
       render_template
       self
     end
 
     def <<(file)
+      @files ||= []
       @files << File.realpath(file) if /\.pdf\Z/ =~ file
     end
 
     def files=(file_array)
-      return unless file_array.is_a? Array
+      return unless file_array.respond_to? :each
 
       file_array.each do |f|
         self << f
diff --git a/lib/jekyll-pandoc-multiple-formats/version.rb b/lib/jekyll-pandoc-multiple-formats/version.rb
index 85518bfd2b89094594182cd48d828e2dcc407185..f06162dead1d74a753522add3d2800bb3cc7574e 100644
--- a/lib/jekyll-pandoc-multiple-formats/version.rb
+++ b/lib/jekyll-pandoc-multiple-formats/version.rb
@@ -1,3 +1,3 @@
 module JekyllPandocMultipleFormats
-  VERSION = '0.2.5'
+  VERSION = '0.2.6'
 end