diff --git a/t/hpke.c b/t/hpke.c
index ca0d4a6..0330064 100644
--- a/t/hpke.c
+++ b/t/hpke.c
@@ -32,14 +32,13 @@
 static ptls_hpke_kem_t *test_kem;
 static ptls_hpke_cipher_suite_t *test_cipher;
 
-
 void test_one_hpke(void)
 {
     static const uint8_t cleartext[] = {0x42, 0x65, 0x61, 0x75, 0x74, 0x79, 0x20, 0x69, 0x73, 0x20, 0x74, 0x72, 0x75, 0x74, 0x68,
                                         0x2c, 0x20, 0x74, 0x72, 0x75, 0x74, 0x68, 0x20, 0x62, 0x65, 0x61, 0x75, 0x74, 0x79},
                          info[] = {0x4f, 0x64, 0x65, 0x20, 0x6f, 0x6e, 0x20, 0x61, 0x20, 0x47,
                                    0x72, 0x65, 0x63, 0x69, 0x61, 0x6e, 0x20, 0x55, 0x72, 0x6e},
-                         aad[] = {0x43, 0x6f, 0x75, 0x6e, 0x74, 0x2d, 0x30};
+                         aad[2][7] = {{0x43, 0x6f, 0x75, 0x6e, 0x74, 0x2d, 0x30}, {0x43, 0x6f, 0x75, 0x6e, 0x74, 0x2d, 0x31}};
     static const struct {
         struct {
             uint16_t kem;
@@ -51,7 +50,7 @@
             size_t len;
         } server_pubkey, client_pubkey, dh;
         uint8_t expected_secret[PTLS_MAX_DIGEST_SIZE];
-        uint8_t expected_ciphertext[sizeof(cleartext) + 32 /* max tag size */];
+        uint8_t expected_ciphertext[2][sizeof(cleartext) + 32 /* max tag size */];
     } all[] =
         {{.id = {PTLS_HPKE_KEM_X25519_SHA256, PTLS_HPKE_HKDF_SHA256, PTLS_HPKE_AEAD_AES_128_GCM},
           .server_pubkey = {{0x39, 0x48, 0xcf, 0xe0, 0xad, 0x1d, 0xdb, 0x69, 0x5d, 0x78, 0x0e, 0x59, 0x07, 0x71, 0x95, 0xda,
@@ -65,9 +64,12 @@
                  32},
           .expected_secret = {0xfe, 0x0e, 0x18, 0xc9, 0xf0, 0x24, 0xce, 0x43, 0x79, 0x9a, 0xe3, 0x93, 0xc7, 0xe8, 0xfe, 0x8f,
                               0xce, 0x9d, 0x21, 0x88, 0x75, 0xe8, 0x22, 0x7b, 0x01, 0x87, 0xc0, 0x4e, 0x7d, 0x2e, 0xa1, 0xfc},
-          .expected_ciphertext = {0xf9, 0x38, 0x55, 0x8b, 0x5d, 0x72, 0xf1, 0xa2, 0x38, 0x10, 0xb4, 0xbe, 0x2a, 0xb4, 0xf8,
-                                  0x43, 0x31, 0xac, 0xc0, 0x2f, 0xc9, 0x7b, 0xab, 0xc5, 0x3a, 0x52, 0xae, 0x82, 0x18, 0xa3,
-                                  0x55, 0xa9, 0x6d, 0x87, 0x70, 0xac, 0x83, 0xd0, 0x7b, 0xea, 0x87, 0xe1, 0x3c, 0x51, 0x2a}},
+          .expected_ciphertext = {{0xf9, 0x38, 0x55, 0x8b, 0x5d, 0x72, 0xf1, 0xa2, 0x38, 0x10, 0xb4, 0xbe, 0x2a, 0xb4, 0xf8,
+                                   0x43, 0x31, 0xac, 0xc0, 0x2f, 0xc9, 0x7b, 0xab, 0xc5, 0x3a, 0x52, 0xae, 0x82, 0x18, 0xa3,
+                                   0x55, 0xa9, 0x6d, 0x87, 0x70, 0xac, 0x83, 0xd0, 0x7b, 0xea, 0x87, 0xe1, 0x3c, 0x51, 0x2a},
+                                  {0xaf, 0x2d, 0x7e, 0x9a, 0xc9, 0xae, 0x7e, 0x27, 0x0f, 0x46, 0xba, 0x1f, 0x97, 0x5b, 0xe5,
+                                   0x3c, 0x09, 0xf8, 0xd8, 0x75, 0xbd, 0xc8, 0x53, 0x54, 0x58, 0xc2, 0x49, 0x4e, 0x8a, 0x6e,
+                                   0xab, 0x25, 0x1c, 0x03, 0xd0, 0xc2, 0x2a, 0x56, 0xb8, 0xca, 0x42, 0xc2, 0x06, 0x3b, 0x84}}},
          {.id = {PTLS_HPKE_KEM_P256_SHA256, PTLS_HPKE_HKDF_SHA256, PTLS_HPKE_AEAD_AES_128_GCM},
           .server_pubkey = {{0x04, 0xfe, 0x8c, 0x19, 0xce, 0x09, 0x05, 0x19, 0x1e, 0xbc, 0x29, 0x8a, 0x92, 0x45, 0x79, 0x25, 0x31,
                              0xf2, 0x6f, 0x0c, 0xec, 0xe2, 0x46, 0x06, 0x39, 0xe8, 0xbc, 0x39, 0xcb, 0x7f, 0x70, 0x6a, 0x82, 0x6a,
@@ -84,9 +86,12 @@
                  32},
           .expected_secret = {0xc0, 0xd2, 0x6a, 0xea, 0xb5, 0x36, 0x60, 0x9a, 0x57, 0x2b, 0x07, 0x69, 0x5d, 0x93, 0x3b, 0x58,
                               0x9d, 0xcf, 0x36, 0x3f, 0xf9, 0xd9, 0x3c, 0x93, 0xad, 0xea, 0x53, 0x7a, 0xea, 0xbb, 0x8c, 0xb8},
-          .expected_ciphertext = {0x5a, 0xd5, 0x90, 0xbb, 0x8b, 0xaa, 0x57, 0x7f, 0x86, 0x19, 0xdb, 0x35, 0xa3, 0x63, 0x11,
-                                  0x22, 0x6a, 0x89, 0x6e, 0x73, 0x42, 0xa6, 0xd8, 0x36, 0xd8, 0xb7, 0xbc, 0xd2, 0xf2, 0x0b,
-                                  0x6c, 0x7f, 0x90, 0x76, 0xac, 0x23, 0x2e, 0x3a, 0xb2, 0x52, 0x3f, 0x39, 0x51, 0x34, 0x34}},
+          .expected_ciphertext = {{0x5a, 0xd5, 0x90, 0xbb, 0x8b, 0xaa, 0x57, 0x7f, 0x86, 0x19, 0xdb, 0x35, 0xa3, 0x63, 0x11,
+                                   0x22, 0x6a, 0x89, 0x6e, 0x73, 0x42, 0xa6, 0xd8, 0x36, 0xd8, 0xb7, 0xbc, 0xd2, 0xf2, 0x0b,
+                                   0x6c, 0x7f, 0x90, 0x76, 0xac, 0x23, 0x2e, 0x3a, 0xb2, 0x52, 0x3f, 0x39, 0x51, 0x34, 0x34},
+                                  {0xfa, 0x6f, 0x03, 0x7b, 0x47, 0xfc, 0x21, 0x82, 0x6b, 0x61, 0x01, 0x72, 0xca, 0x96, 0x37,
+                                   0xe8, 0x2d, 0x6e, 0x58, 0x01, 0xeb, 0x31, 0xcb, 0xd3, 0x74, 0x82, 0x71, 0xaf, 0xfd, 0x4e,
+                                   0xcb, 0x06, 0x64, 0x6e, 0x03, 0x29, 0xcb, 0xdf, 0x3c, 0x3c, 0xd6, 0x55, 0xb2, 0x8e, 0x82}}},
          {.id = {PTLS_HPKE_KEM_P256_SHA256, PTLS_HPKE_HKDF_SHA512, PTLS_HPKE_AEAD_AES_128_GCM},
           .server_pubkey = {{0x04, 0x08, 0x5a, 0xa5, 0xb6, 0x65, 0xdc, 0x38, 0x26, 0xf9, 0x65, 0x0c, 0xcb, 0xcc, 0x47, 0x1b, 0xe2,
                              0x68, 0xc8, 0xad, 0xa8, 0x66, 0x42, 0x2f, 0x73, 0x9e, 0x2d, 0x53, 0x1d, 0x4a, 0x88, 0x18, 0xa9, 0x46,
@@ -103,16 +108,19 @@
                  32},
           .expected_secret = {0x02, 0xf5, 0x84, 0x73, 0x63, 0x90, 0xfc, 0x93, 0xf5, 0xb4, 0xad, 0x03, 0x98, 0x26, 0xa3, 0xfa,
                               0x08, 0xe9, 0x91, 0x1b, 0xd1, 0x21, 0x5a, 0x3d, 0xb8, 0xe8, 0x79, 0x1b, 0xa5, 0x33, 0xca, 0xfd},
-          .expected_ciphertext = {0xd3, 0xcf, 0x49, 0x84, 0x93, 0x14, 0x84, 0xa0, 0x80, 0xf7, 0x4c, 0x1b, 0xb2, 0xa6, 0x78,
-                                  0x27, 0x00, 0xdc, 0x1f, 0xef, 0x9a, 0xbe, 0x84, 0x42, 0xe4, 0x4a, 0x6f, 0x09, 0x04, 0x4c,
-                                  0x88, 0x90, 0x72, 0x00, 0xb3, 0x32, 0x00, 0x35, 0x43, 0x75, 0x4e, 0xb5, 0x19, 0x17, 0xba}},
-            {{0}}}, *test;
+          .expected_ciphertext = {{0xd3, 0xcf, 0x49, 0x84, 0x93, 0x14, 0x84, 0xa0, 0x80, 0xf7, 0x4c, 0x1b, 0xb2, 0xa6, 0x78,
+                                   0x27, 0x00, 0xdc, 0x1f, 0xef, 0x9a, 0xbe, 0x84, 0x42, 0xe4, 0x4a, 0x6f, 0x09, 0x04, 0x4c,
+                                   0x88, 0x90, 0x72, 0x00, 0xb3, 0x32, 0x00, 0x35, 0x43, 0x75, 0x4e, 0xb5, 0x19, 0x17, 0xba},
+                                  {0xd1, 0x44, 0x14, 0x55, 0x5a, 0x47, 0x26, 0x9d, 0xfe, 0xad, 0x9f, 0xbf, 0x26, 0xab, 0xb3,
+                                   0x03, 0x36, 0x5e, 0x40, 0x70, 0x9a, 0x4e, 0xd1, 0x6e, 0xae, 0xfe, 0x1f, 0x20, 0x70, 0xf1,
+                                   0xdd, 0xeb, 0x1b, 0xdd, 0x94, 0xd9, 0xe4, 0x11, 0x86, 0xf1, 0x24, 0xe0, 0xac, 0xc6, 0x2d}}},
+         {{0}}},
+      *test;
     int ret;
 
     /* find the corresponding test vector or bail out if not found */
     for (test = all;
-         !(test->id.kem == test_kem->id && test->id.kdf == test_cipher->id.kdf && test->id.aead == test_cipher->id.aead);
-         ++test) {
+         !(test->id.kem == test_kem->id && test->id.kdf == test_cipher->id.kdf && test->id.aead == test_cipher->id.aead); ++test) {
         if (test->id.kem == 0) {
             note("no test vector for given kem / cipher");
             return;
@@ -133,9 +141,11 @@
         uint8_t ciphertext[sizeof(cleartext) + 32];
         ret = key_schedule(test_kem, test_cipher, &enc, 1, test->expected_secret, ptls_iovec_init(info, sizeof(info)));
         ok(ret == 0);
-        ptls_aead_encrypt(enc, ciphertext, cleartext, sizeof(cleartext), 0, aad, sizeof(aad));
+        for (uint64_t seq = 0; seq < 2; ++seq) {
+            ptls_aead_encrypt(enc, ciphertext, cleartext, sizeof(cleartext), seq, aad[seq], sizeof(aad[seq]));
+            ok(memcmp(ciphertext, test->expected_ciphertext[seq], sizeof(cleartext) + test_cipher->aead->tag_size) == 0);
+        }
         ptls_aead_free(enc);
-        ok(memcmp(ciphertext, test->expected_ciphertext, sizeof(cleartext) + test_cipher->aead->tag_size) == 0);
     }
 
     { /* decryption */
@@ -143,10 +153,13 @@
         uint8_t text_recovered[sizeof(cleartext)];
         ret = key_schedule(test_kem, test_cipher, &dec, 0, test->expected_secret, ptls_iovec_init(info, sizeof(info)));
         ok(ret == 0);
-        ok(ptls_aead_decrypt(dec, text_recovered, test->expected_ciphertext, sizeof(text_recovered) + test_cipher->aead->tag_size, 0,
-                             aad, sizeof(aad)) == sizeof(cleartext));
+        for (uint64_t seq = 0; seq < 2; ++seq) {
+            ok(ptls_aead_decrypt(dec, text_recovered, test->expected_ciphertext[seq],
+                                 sizeof(text_recovered) + test_cipher->aead->tag_size, seq, aad[seq],
+                                 sizeof(aad[seq])) == sizeof(cleartext));
+            ok(memcmp(text_recovered, cleartext, sizeof(cleartext)) == 0);
+        }
         ptls_aead_free(dec);
-        ok(memcmp(text_recovered, cleartext, sizeof(cleartext)) == 0);
     }
 }