diff --git a/include/polarssl/md4.h b/include/polarssl/md4.h
index 5a796ae..2bd35ea 100644
--- a/include/polarssl/md4.h
+++ b/include/polarssl/md4.h
@@ -29,6 +29,8 @@
 
 #include <string.h>
 
+#define POLARSSL_ERR_MD4_FILE_IO_ERROR                 -0x0072  /**< Read/write error in file. */
+
 /**
  * \brief          MD4 context structure
  */
@@ -86,8 +88,7 @@
  * \param path     input file name
  * \param output   MD4 checksum result
  *
- * \return         0 if successful, 1 if fopen failed,
- *                 or 2 if fread failed
+ * \return         0 if successful, or POLARSSL_ERR_MD4_FILE_IO_ERROR
  */
 int md4_file( const char *path, unsigned char output[16] );