diff --git a/fs/fat/ff.c b/fs/fat/ff.c
index 345c174155d1..478daa7d6b0b 100644
--- a/fs/fat/ff.c
+++ b/fs/fat/ff.c
@@ -1374,6 +1374,7 @@ void fit_lfn (
 /*-----------------------------------------------------------------------*/
 /* Create numbered name                                                  */
 /*-----------------------------------------------------------------------*/
+#if !_FS_READONLY
 #if _USE_LFN
 static
 void gen_numname (
@@ -1426,6 +1427,7 @@ void gen_numname (
 	} while (j < 8);
 }
 #endif
+#endif