diff --git a/lib/openapi_first/response_parser.rb b/lib/openapi_first/response_parser.rb
index d406ccde..90666173 100644
--- a/lib/openapi_first/response_parser.rb
+++ b/lib/openapi_first/response_parser.rb
@@ -25,7 +25,7 @@ def read_body(rack_response)
       buffered_body = +''
 
       if rack_response.body.respond_to?(:each)
-        rack_response.body.each { |chunk| buffered_body.to_s << chunk }
+        rack_response.body.each { |chunk| buffered_body << chunk }
         return buffered_body
       end
       rack_response.body