diff --git a/library/x509write_csr.c b/library/x509write_csr.c
index 8fd856b..fd22c28 100644
--- a/library/x509write_csr.c
+++ b/library/x509write_csr.c
@@ -194,14 +194,21 @@
      */
     mbedtls_md( mbedtls_md_info_from_type( ctx->md_alg ), c, len, hash );
 
-    pk_alg = mbedtls_pk_get_type( ctx->key );
-    if( pk_alg == MBEDTLS_PK_ECKEY )
-        pk_alg = MBEDTLS_PK_ECDSA;
-
     if( ( ret = mbedtls_pk_sign( ctx->key, ctx->md_alg, hash, 0, sig, &sig_len,
-                         f_rng, p_rng ) ) != 0 ||
-        ( ret = mbedtls_oid_get_oid_by_sig_alg( pk_alg, ctx->md_alg,
-                                        &sig_oid, &sig_oid_len ) ) != 0 )
+                                 f_rng, p_rng ) ) != 0 )
+    {
+        return( ret );
+    }
+
+    if( mbedtls_pk_can_do( ctx->key, MBEDTLS_PK_RSA ) )
+        pk_alg = MBEDTLS_PK_RSA;
+    else if( mbedtls_pk_can_do( ctx->key, MBEDTLS_PK_ECDSA ) )
+        pk_alg = MBEDTLS_PK_ECDSA;
+    else
+        pk_alg = MBEDTLS_PK_NONE;
+
+    if( ( ret = mbedtls_oid_get_oid_by_sig_alg( pk_alg, ctx->md_alg,
+                                                &sig_oid, &sig_oid_len ) ) != 0 )
     {
         return( ret );
     }