diff --git a/include/polarssl/oid.h b/include/polarssl/oid.h
index 025a15f..b0e781f 100644
--- a/include/polarssl/oid.h
+++ b/include/polarssl/oid.h
@@ -409,11 +409,12 @@
  * \param md_alg   message digest algorithm
  * \param pk_alg   public key algorithm
  * \param oid      place to store ASN.1 OID string pointer
+ * \param olen     length of the OID
  *
  * \return         0 if successful, or POLARSSL_ERR_OID_NOT_FOUND
  */
 int oid_get_oid_by_sig_alg( pk_type_t pk_alg, md_type_t md_alg,
-                            const char **oid_str );
+                            const char **oid, size_t *olen );
 
 /**
  * \brief          Translate hash algorithm OID into md_type
@@ -441,10 +442,11 @@
  *
  * \param md_alg   message digest algorithm
  * \param oid      place to store ASN.1 OID string pointer
+ * \param olen     length of the OID
  *
  * \return         0 if successful, or POLARSSL_ERR_OID_NOT_FOUND
  */
-int oid_get_oid_by_md( md_type_t md_alg, const char **oid_str );
+int oid_get_oid_by_md( md_type_t md_alg, const char **oid, size_t *olen );
 
 #if defined(POLARSSL_CIPHER_C)
 /**