diff --git a/hdr/file.h b/hdr/file.h
index 1c205ba..2a33a42 100644
--- a/hdr/file.h
+++ b/hdr/file.h
@@ -50,6 +50,7 @@ static BYTE *file_hRcsId =
 #define O_RDONLY        SFT_MREAD
 #define O_WRONLY        SFT_MWRITE
 #define O_RDWR          SFT_MRDWR
+#define O_ACCMODE       3
 
 /* bits 2, 3 reserved */
 /* bits 4, 5, 6 sharing modes */
diff --git a/kernel/fatfs.c b/kernel/fatfs.c
index 8901584..6adb8fe 100644
--- a/kernel/fatfs.c
+++ b/kernel/fatfs.c
@@ -150,7 +150,7 @@ long dos_open(char *path, unsigned flags, unsigned attrib)
 
   /* First test the flags to see if the user has passed a valid   */
   /* file mode...                                                 */
-  if ((flags & 3) > 2)
+  if ((flags & O_ACCMODE) > 2)
     return DE_INVLDACC;
 
   /* first split the passed dir into comopnents (i.e. - path to   */
@@ -187,7 +187,8 @@ long dos_open(char *path, unsigned flags, unsigned attrib)
         flags = (flags & ~3) | O_RDONLY;
 
       /* Check permissions. -- JPP */
-      if ((fnp->f_dir.dir_attrib & D_RDONLY) && ((flags & 3) != O_RDONLY))
+      if ((fnp->f_dir.dir_attrib & D_RDONLY) &&
+          ((flags & O_ACCMODE) != O_RDONLY))
       {
         dir_close(fnp);
         return DE_ACCESS;
@@ -219,8 +220,8 @@ long dos_open(char *path, unsigned flags, unsigned attrib)
   
   /* Set the fnode to the desired mode                    */
   /* Updating the directory entry first.                  */
-  fnp->f_mode = flags & 3;
-    
+  fnp->f_mode = flags & O_ACCMODE;
+
   if (status != S_OPENED)
   {
     init_direntry(&fnp->f_dir, attrib, FREE);