diff --git a/include/polarssl/x509.h b/include/polarssl/x509.h
index fe4379512..17d99af82 100644
--- a/include/polarssl/x509.h
+++ b/include/polarssl/x509.h
@@ -549,6 +549,7 @@ const char *x509_oid_get_description( x509_buf *oid );
 
 /**
  * \brief          Give an OID, return a string version of its OID number.
+ *                 (Deprecated. Use oid_get_numeric_string() instead)
  *
  * \param buf      Buffer to write to
  * \param size     Maximum size of buffer