diff --git a/lib/openai/internal/util.rb b/lib/openai/internal/util.rb
index 429fbaf7..9f1e6d10 100644
--- a/lib/openai/internal/util.rb
+++ b/lib/openai/internal/util.rb
@@ -540,8 +540,7 @@ class << self
           y << "Content-Disposition: form-data"
 
           unless key.nil?
-            name = ERB::Util.url_encode(key.to_s)
-            y << "; name=\"#{name}\""
+            y << "; name=\"#{key}\""
           end
 
           case val
@@ -577,7 +576,7 @@ class << self
                 case val
                 in Array if val.all? { primitive?(_1) }
                   val.each do |v|
-                    write_multipart_chunk(y, boundary: boundary, key: key, val: v, closing: closing)
+                    write_multipart_chunk(y, boundary: boundary, key: "#{key}[]", val: v, closing: closing)
                   end
                 else
                   write_multipart_chunk(y, boundary: boundary, key: key, val: val, closing: closing)