diff --git a/lib/annotate/parser.rb b/lib/annotate/parser.rb
index cb27b8b5..ad025f40 100644
--- a/lib/annotate/parser.rb
+++ b/lib/annotate/parser.rb
@@ -56,7 +56,7 @@ def add_options_to_parser(option_parser) # rubocop:disable Metrics/MethodLength
       option_parser.on('--additional-file-patterns path1,path2,path3',
                        Array,
                        "Additional file paths or globs to annotate, separated by commas (e.g. `/foo/bar/%model_name%/*.rb,/baz/%model_name%.rb`)") do |additional_file_patterns|
-        ENV['additional_file_patterns'] = additional_file_patterns
+        env['additional_file_patterns'] = additional_file_patterns.join(',')
       end
 
       option_parser.on('-d',