diff --git a/lib/annotate/parser.rb b/lib/annotate/parser.rb
index ad85caf5..b39fbd0b 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',
diff --git a/lib/annotate/version.rb b/lib/annotate/version.rb
index e103c6b8..f63d8a3e 100644
--- a/lib/annotate/version.rb
+++ b/lib/annotate/version.rb
@@ -1,5 +1,5 @@
 module Annotate
   def self.version
-    '3.2.0'
+    '3.2.1'
   end
 end
diff --git a/spec/lib/annotate/parser_spec.rb b/spec/lib/annotate/parser_spec.rb
index 16084b02..f420804b 100644
--- a/spec/lib/annotate/parser_spec.rb
+++ b/spec/lib/annotate/parser_spec.rb
@@ -20,7 +20,7 @@ module Annotate # rubocop:disable Metrics/ModuleLength
           paths = 'foo/bar,baz'
           allow(ENV).to receive(:[]=)
           Parser.parse([option, paths])
-          expect(ENV).to have_received(:[]=).with('additional_file_patterns', ['foo/bar', 'baz'])
+          expect(ENV).to have_received(:[]=).with('additional_file_patterns', 'foo/bar,baz')
         end
       end
     end