diff --git a/src/ff.c b/src/ff.c
index 9c887c4..55b7f04 100644
--- a/src/ff.c
+++ b/src/ff.c
@@ -163,8 +163,11 @@
 
 
 /* Timestamp feature */
-#if _FS_NORTC
-#define GET_FATTIME()	((DWORD)_NORTC_YEAR << 25 | (DWORD)_NORTC_MON << 21 | (DWORD)_NORTC_MDAY << 16)
+#if _FS_NORTC == 1
+#if _NORTC_YEAR < 1980 || _NORTC_YEAR > 2107 || _NORTC_MON < 1 || _NORTC_MON > 12 || _NORTC_MDAY < 1 || _NORTC_MDAY > 31
+#error Invalid _FS_NORTC settings
+#endif
+#define GET_FATTIME()	((DWORD)(_NORTC_YEAR - 1980) << 25 | (DWORD)_NORTC_MON << 21 | (DWORD)_NORTC_MDAY << 16)
 #else
 #define GET_FATTIME()	get_fattime()
 #endif