diff --git a/components/libc/compilers/armlibc/sys/unistd.h b/components/libc/compilers/armlibc/sys/unistd.h
index 3199b01e0e..524de2cf83 100644
--- a/components/libc/compilers/armlibc/sys/unistd.h
+++ b/components/libc/compilers/armlibc/sys/unistd.h
@@ -36,16 +36,34 @@
 #define _FNDELAY    _FNONBLOCK  /* non blocking I/O (4.2 style) */
 #define _FNOCTTY    0x8000  /* don't assign a ctty on this open */
 
+
+#ifndef O_RDONLY
 #define O_RDONLY    0       /* +1 == FREAD */
+#endif
+#ifndef O_WRONLY
 #define O_WRONLY    1       /* +1 == FWRITE */
+#endif
+#ifndef O_RDWR
 #define O_RDWR      2       /* +1 == FREAD|FWRITE */
+#endif
+#ifndef O_APPEND
 #define O_APPEND    _FAPPEND
+#endif
+#ifndef O_CREAT
 #define O_CREAT     _FCREAT
+#endif
+#ifndef O_TRUNC
 #define O_TRUNC     _FTRUNC
+#endif
+#ifndef O_EXCL
 #define O_EXCL      _FEXCL
+#endif
+#ifndef O_SYNC
 #define O_SYNC      _FSYNC
 #endif
 
+#endif
+
 
 int     isatty      (int fd);
 char *  ttyname     (int desc);