diff --git a/include/mbedtls/x509.h b/include/mbedtls/x509.h
index 8fd321a..f00f3a6 100644
--- a/include/mbedtls/x509.h
+++ b/include/mbedtls/x509.h
@@ -361,7 +361,8 @@
                              mbedtls_asn1_named_data *first);
 int mbedtls_x509_write_sig(unsigned char **p, unsigned char *start,
                            const char *oid, size_t oid_len,
-                           unsigned char *sig, size_t size);
+                           unsigned char *sig, size_t size,
+                           mbedtls_pk_type_t pk_alg);
 
 #define MBEDTLS_X509_SAFE_SNPRINTF                          \
     do {                                                    \