diff --git a/internal-flt.h b/internal-flt.h
new file mode 100644
index 0000000..e47dbb1
--- /dev/null
+++ b/internal-flt.h
@@ -0,0 +1,53 @@
+/* internal-flt.h -- common header file for the internal FLT API.
+   Copyright (C) 2007
+     National Institute of Advanced Industrial Science and Technology (AIST)
+     Registration Number H15PRO112
+
+   This file is part of the m17n library.
+
+   The m17n library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public License
+   as published by the Free Software Foundation; either version 2.1 of
+   the License, or (at your option) any later version.
+
+   The m17n library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the m17n library; if not, write to the Free
+   Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+   02111-1307, USA.  */
+
+#ifndef _M_INTERNAL_FLT_H
+#define _M_INTERNAL_FLT_H
+
+#define MAKE_COMBINING_CODE(base_y, base_x, add_y, add_x, off_y, off_x)	\
+  (((off_y) << 16)							\
+   | ((off_x) << 8)							\
+   | ((base_x) << 6)							\
+   | ((base_y) << 4)							\
+   | ((add_x) << 2)							\
+   | (add_y))
+
+#define COMBINING_CODE_OFF_Y(code) ((((code) >> 16) & 0xFF) - 128)
+#define COMBINING_CODE_OFF_X(code) ((((code) >> 8) & 0xFF) - 128)
+#define COMBINING_CODE_BASE_X(code) (((code) >> 6) & 0x3)
+#define COMBINING_CODE_BASE_Y(code) (((code) >> 4) & 0x3)
+#define COMBINING_CODE_ADD_X(code) (((code) >> 2) & 0x3)
+#define COMBINING_CODE_ADD_Y(code) ((code) & 0x3)
+
+#define MAKE_COMBINING_CODE_BY_CLASS(class) (0x1000000 | class)
+
+#define COMBINING_BY_CLASS_P(code) ((code) & 0x1000000)
+
+#define COMBINING_CODE_CLASS(code) ((code) & 0xFFFFFF)
+
+#define MAKE_PRECOMPUTED_COMBINDING_CODE() (0x2000000)
+
+#define COMBINING_PRECOMPUTED_P(code) ((code) & 0x2000000)
+
+extern MSymbol Mcombining;
+
+#endif /* _M_INTERNAL_FLT_H */