diff --git a/lib/openssl/config.rb b/lib/openssl/config.rb
index 9a0b7874..c96cb7cc 100644
--- a/lib/openssl/config.rb
+++ b/lib/openssl/config.rb
@@ -14,6 +14,8 @@
 require 'stringio'
 
 module OpenSSL
+  class ConfigError;end
+
   ##
   # = OpenSSL::Config
   #
@@ -27,6 +29,9 @@ module OpenSSL
   class Config
     include Enumerable
 
+    # on MRI this constant is set by calling the openssl C function: CONF_get1_default_config_file
+    DEFAULT_CONFIG_FILE = nil
+
     class << self
 
       ##