diff --git a/lib/httpi/adapter/net_http.rb b/lib/httpi/adapter/net_http.rb
index 59d8f96..1274efb 100644
--- a/lib/httpi/adapter/net_http.rb
+++ b/lib/httpi/adapter/net_http.rb
@@ -7,6 +7,7 @@
 
 begin
   require 'net/ntlm'
+  require 'net/ntlm/version' unless Net::NTLM.const_defined?(:VERSION)
   unless Net::NTLM::VERSION::STRING >= '0.3.2'
     raise ArgumentError('Invalid version of rubyntlm. Please use v0.3.2+.')
   end