diff --git a/ruby/pack.c b/ruby/pack.c
index c09bf0f1..1c65c568 100644
--- a/ruby/pack.c
+++ b/ruby/pack.c
@@ -40,9 +40,10 @@ static ID s_append;
 #include "msgpack/pack_template.h"
 
 
-#ifdef HAVE_RUBY_ST_H
-#include "ruby/st.h"  // ruby hash
-#endif
+#if defined(HAVE_RUBY_ST_H)
+#include "ruby/st.h"  // ruby hash on Ruby 1.9
+#elif defined(HAVE_ST_H)
+#include "st.h"       // ruby hash on Ruby 1.8
 
 #define ARG_BUFFER(name, argc, argv) \
 	VALUE name; \