diff --git a/ruby/extconf.rb b/ruby/extconf.rb
index 10a807e7..4082a92f 100644
--- a/ruby/extconf.rb
+++ b/ruby/extconf.rb
@@ -1,5 +1,6 @@
 require 'mkmf'
 require './version.rb'
 $CFLAGS << %[ -I.. -Wall -O3 -DMESSAGEPACK_VERSION=\\"#{MessagePack::VERSION}\\" -g]
+have_header("ruby/st.h")
 create_makefile('msgpack')
 
diff --git a/ruby/pack.c b/ruby/pack.c
index 35717090..c09bf0f1 100644
--- a/ruby/pack.c
+++ b/ruby/pack.c
@@ -40,8 +40,8 @@ static ID s_append;
 #include "msgpack/pack_template.h"
 
 
-#ifndef RUBY_VM
-#include "st.h"  // ruby hash
+#ifdef HAVE_RUBY_ST_H
+#include "ruby/st.h"  // ruby hash
 #endif
 
 #define ARG_BUFFER(name, argc, argv) \