diff --git a/lib/grape/middleware/formatter.rb b/lib/grape/middleware/formatter.rb
index e9e26bac5..3bf31267b 100644
--- a/lib/grape/middleware/formatter.rb
+++ b/lib/grape/middleware/formatter.rb
@@ -40,7 +40,7 @@ def after
           throw :error, status: 500, message: e.message
         end
         headers[Grape::Http::Headers::CONTENT_TYPE] = content_type_for(env['api.format']) unless headers[Grape::Http::Headers::CONTENT_TYPE]
-        Rack::Response.new(bodymap, status, headers).to_a
+        Rack::Response.new(bodymap, status, headers)
       end
 
       private
diff --git a/spec/grape/middleware/formatter_spec.rb b/spec/grape/middleware/formatter_spec.rb
index 419d8911e..35340835d 100644
--- a/spec/grape/middleware/formatter_spec.rb
+++ b/spec/grape/middleware/formatter_spec.rb
@@ -21,7 +21,7 @@ def to_json
         end
       end
 
-      subject.call('PATH_INFO' => '/somewhere', 'HTTP_ACCEPT' => 'application/json').last.each { |b| expect(b).to eq('"bar"') }
+      subject.call('PATH_INFO' => '/somewhere', 'HTTP_ACCEPT' => 'application/json').to_a.last.each { |b| expect(b).to eq('"bar"') }
     end
 
     it 'calls #to_json if the content type is jsonapi' do
@@ -32,7 +32,7 @@ def to_json
         end
       end
 
-      subject.call('PATH_INFO' => '/somewhere', 'HTTP_ACCEPT' => 'application/vnd.api+json').last.each { |b| expect(b).to eq('{"foos":[{"bar":"baz"}] }') }
+      subject.call('PATH_INFO' => '/somewhere', 'HTTP_ACCEPT' => 'application/vnd.api+json').to_a.last.each { |b| expect(b).to eq('{"foos":[{"bar":"baz"}] }') }
     end
 
     it 'calls #to_xml if the content type is xml' do
@@ -43,7 +43,7 @@ def to_xml
         end
       end
 
-      subject.call('PATH_INFO' => '/somewhere.xml', 'HTTP_ACCEPT' => 'application/json').last.each { |b| expect(b).to eq('<bar/>') }
+      subject.call('PATH_INFO' => '/somewhere.xml', 'HTTP_ACCEPT' => 'application/json').to_a.last.each { |b| expect(b).to eq('<bar/>') }
     end
   end