diff --git a/librb/configure.ac b/librb/configure.ac
index a0fefbae..0e434c93 100644
--- a/librb/configure.ac
+++ b/librb/configure.ac
@@ -63,6 +63,7 @@ case "$host_os" in
      AC_DEFINE_UNQUOTED(WINDOWS,1,[This is a Windows system])
      ;;
 *mingw*)
+*msys*)
      AC_DEFINE_UNQUOTED(MINGW,1,[This is a MinGW system])
      AC_DEFINE_UNQUOTED(WINDOWS,1,[This is a Windows system])
      AC_CHECK_HEADER(windows.h, , [AC_MSG_ERROR([** MinGW and no windows.h.  I give up.])])