diff --git a/tests/suites/test_suite_ecp.function b/tests/suites/test_suite_ecp.function
index c061275..ef0781b 100644
--- a/tests/suites/test_suite_ecp.function
+++ b/tests/suites/test_suite_ecp.function
@@ -1204,27 +1204,40 @@
         TEST_EQUAL(mbedtls_mpi_cmp_int(&key.Q.Y, 2), 0);
         TEST_EQUAL(mbedtls_mpi_cmp_int(&key.Q.Z, 3), 0);
 
-        if (canonical) {
+        if (canonical && in_key->len == (key.grp.nbits + 7) / 8) {
             unsigned char buf[MBEDTLS_ECP_MAX_BYTES];
+            size_t length = 0xdeadbeef;
 
-            ret = mbedtls_ecp_write_key(&key, buf, in_key->len);
-            TEST_ASSERT(ret == 0);
+            TEST_EQUAL(mbedtls_ecp_write_key_ext(&key,
+                                                 &length, buf, in_key->len), 0);
+            TEST_MEMORY_COMPARE(in_key->x, in_key->len,
+                                buf, length);
 
+            memset(buf, 0, sizeof(buf));
+            TEST_EQUAL(mbedtls_ecp_write_key(&key, buf, in_key->len), 0);
             TEST_MEMORY_COMPARE(in_key->x, in_key->len,
                                 buf, in_key->len);
         } else {
             unsigned char export1[MBEDTLS_ECP_MAX_BYTES];
             unsigned char export2[MBEDTLS_ECP_MAX_BYTES];
 
-            ret = mbedtls_ecp_write_key(&key, export1, in_key->len);
-            TEST_ASSERT(ret == 0);
+            size_t length1 = 0xdeadbeef;
+            TEST_EQUAL(mbedtls_ecp_write_key_ext(&key, &length1,
+                                                 export1, sizeof(export1)), 0);
+            TEST_EQUAL(mbedtls_ecp_read_key(grp_id, &key2, export1, length1),
+                       expected);
+            size_t length2 = 0xdeadbeef;
+            TEST_EQUAL(mbedtls_ecp_write_key_ext(&key2, &length2,
+                                                 export2, sizeof(export2)), 0);
+            TEST_MEMORY_COMPARE(export1, length1,
+                                export2, length2);
 
-            ret = mbedtls_ecp_read_key(grp_id, &key2, export1, in_key->len);
-            TEST_ASSERT(ret == expected);
-
-            ret = mbedtls_ecp_write_key(&key2, export2, in_key->len);
-            TEST_ASSERT(ret == 0);
-
+            memset(export1, 0, sizeof(export1));
+            memset(export2, 0, sizeof(export2));
+            TEST_EQUAL(mbedtls_ecp_write_key(&key, export1, in_key->len), 0);
+            TEST_EQUAL(mbedtls_ecp_read_key(grp_id, &key2, export1, in_key->len),
+                       expected);
+            TEST_EQUAL(mbedtls_ecp_write_key(&key2, export2, in_key->len), 0);
             TEST_MEMORY_COMPARE(export1, in_key->len,
                                 export2, in_key->len);
         }