diff --git a/library/pk.c b/library/pk.c
index 2c0ef68..580fa0e 100644
--- a/library/pk.c
+++ b/library/pk.c
@@ -1021,7 +1021,7 @@
         psa_key_attributes_t attributes = PSA_KEY_ATTRIBUTES_INIT;
         psa_algorithm_t psa_sig_alg = PSA_ALG_RSA_PSS_ANY_SALT(psa_md_alg);
         p = buf + sizeof(buf);
-        key_len = mbedtls_pk_write_pubkey(&p, buf, ctx);
+        key_len = mbedtls_rsa_write_pubkey(mbedtls_pk_rsa(*ctx), buf, &p);
 
         if (key_len < 0) {
             return key_len;