- Functions requiring File System functions can now be disables by undefining POLARSSL_FS_IO

diff --git a/include/polarssl/md.h b/include/polarssl/md.h
index 9bda3ee..57a0d6a 100644
--- a/include/polarssl/md.h
+++ b/include/polarssl/md.h
@@ -36,6 +36,8 @@
 #define inline _inline
 #endif
 
+#define POLARSSL_ERR_MD_FEATURE_UNAVAILABLE                     -0x0830
+
 typedef enum {
     POLARSSL_MD_NONE=0,
     POLARSSL_MD_MD2,