diff --git a/ext/RMagick/extconf.rb b/ext/RMagick/extconf.rb
index 52ea28211..929d9273c 100644
--- a/ext/RMagick/extconf.rb
+++ b/ext/RMagick/extconf.rb
@@ -1,3 +1,5 @@
+lib_dir = File.expand_path('../../lib', File.dirname(__FILE__))
+$LOAD_PATH.unshift(lib_dir) unless $LOAD_PATH.include?(lib_dir)
 require 'mkmf'
 require 'date'