diff --git a/ChangeLog b/ChangeLog
index 20f5eda9bd..716c26fe2d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Sun Aug 17 15:58:08 2008  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* lib/mkmf.rb (init_mkmf): add include/ruby/backward to $INCFLAGS.
+
+	* include/ruby/backward/{st,util}.h: added for backward compatibility.
+	  [ruby-dev:35811]
+
 Sun Aug 17 13:40:04 2008  Tanaka Akira  <akr@fsij.org>
 
 	* transcode.c (econv_primitive_putback): new method.
diff --git a/include/ruby/backward/st.h b/include/ruby/backward/st.h
new file mode 100644
index 0000000000..514128e616
--- /dev/null
+++ b/include/ruby/backward/st.h
@@ -0,0 +1,6 @@
+#if   defined __GNUC__
+#warning use "ruby/st.h" instead of bare "st.h"
+#elif defined _MSC_VER || defined __BORLANDC__
+#pragma message("warning: use \"ruby/st.h\" instead of bare \"st.h\"")
+#endif
+#include "ruby/st.h"
diff --git a/include/ruby/backward/util.h b/include/ruby/backward/util.h
new file mode 100644
index 0000000000..6b47940ddc
--- /dev/null
+++ b/include/ruby/backward/util.h
@@ -0,0 +1,6 @@
+#if   defined __GNUC__
+#warning use "ruby/util.h" instead of bare "util.h"
+#elif defined _MSC_VER || defined __BORLANDC__
+#pragma message("warning: use \"ruby/util.h\" instead of bare \"util.h\"")
+#endif
+#include "ruby/util.h"
diff --git a/lib/mkmf.rb b/lib/mkmf.rb
index df8861a71e..c4b5b59c54 100644
--- a/lib/mkmf.rb
+++ b/lib/mkmf.rb
@@ -1757,7 +1757,9 @@ def init_mkmf(config = CONFIG)
   $ARCH_FLAG = with_config("arch_flag", arg_config("ARCH_FLAG", config["ARCH_FLAG"])).dup
   $CPPFLAGS = with_config("cppflags", arg_config("CPPFLAGS", config["CPPFLAGS"])).dup
   $LDFLAGS = with_config("ldflags", arg_config("LDFLAGS", config["LDFLAGS"])).dup
-  $INCFLAGS = "-I$(arch_hdrdir) -I$(hdrdir) -I$(srcdir)"
+  $INCFLAGS = "-I$(arch_hdrdir)"
+  $INCFLAGS << " -I$(hdrdir)/ruby/backward" unless $extmk
+  $INCFLAGS << " -I$(hdrdir) -I$(srcdir)"
   $DLDFLAGS = with_config("dldflags", arg_config("DLDFLAGS", config["DLDFLAGS"])).dup
   $LIBEXT = config['LIBEXT'].dup
   $OBJEXT = config["OBJEXT"].dup