diff --git a/ChangeLog b/ChangeLog
index 10744c4da4..814789a7d3 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,4 +1,7 @@
-Thu Aug  9 23:46:47 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+Thu Aug  9 23:46:51 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* tool/mkrunnable.rb: see build_os instead of target arch for
+	  cross-compiling.
 
 	* configure.in (MINIRUBY): use real path for include path.
 
diff --git a/tool/mkrunnable.rb b/tool/mkrunnable.rb
index 6a6a92658a..35b75ec934 100755
--- a/tool/mkrunnable.rb
+++ b/tool/mkrunnable.rb
@@ -34,7 +34,7 @@ end
 
 alias ln_dir_safe ln_safe
 
-if /mingw|mswin/ =~ RUBY_PLATFORM
+if /mingw|mswin/ =~ RbConfig::CONFIG["build_os"]
   extend Mswin
 end