diff --git a/lib/httparty/hash_conversions.rb b/lib/httparty/hash_conversions.rb
index 270effe3..a888db0e 100644
--- a/lib/httparty/hash_conversions.rb
+++ b/lib/httparty/hash_conversions.rb
@@ -54,11 +54,9 @@ def self.normalize_keys(key, value)
       stack.each do |parent, hash|
         hash.each do |child_key, child_value|
           if child_value.respond_to?(:to_hash)
-            stack << ["#{parent}[#{child_key}]", child_value.to_hash]
+            normalized_keys += normalize_keys("#{parent}[#{child_key}]", child_value)
           elsif child_value.respond_to?(:to_ary)
-            child_value.to_ary.each do |v|
-              normalized_keys << normalize_keys("#{parent}[#{child_key}][]", v).flatten
-            end
+            normalized_keys += normalize_keys("#{parent}[#{child_key}]", child_value)
           else
             normalized_keys << normalize_keys("#{parent}[#{child_key}]", child_value).flatten
           end