diff --git a/lib/em-http/http_encoding.rb b/lib/em-http/http_encoding.rb
index cf7e647..af198e6 100644
--- a/lib/em-http/http_encoding.rb
+++ b/lib/em-http/http_encoding.rb
@@ -126,7 +126,7 @@ def encode_auth(k,v)
     end
 
     def encode_headers(head)
-      head.inject('') do |result, (key, value)|
+      head.inject(String.new) do |result, (key, value)|
         # Munge keys from foo-bar-baz to Foo-Bar-Baz
         key = key.split('-').map { |k| k.to_s.capitalize }.join('-')
         result << case key
@@ -140,7 +140,7 @@ def encode_headers(head)
 
     def encode_cookie(cookie)
       if cookie.is_a? Hash
-        cookie.inject('') { |result, (k, v)| result <<  encode_param(k, v) + ";" }
+        cookie.inject(String.new) { |result, (k, v)| result <<  encode_param(k, v) + ";" }
       else
         cookie
       end