diff --git a/src/test/unit/unit_esp.c b/src/test/unit/unit_esp.c
index 05f21db..f648c30 100644
--- a/src/test/unit/unit_esp.c
+++ b/src/test/unit/unit_esp.c
@@ -503,6 +503,55 @@ START_TEST(test_replay_old_seqs_after_jump)
 }
 END_TEST
 
+/* The transmitted sequence number must never be allowed to overflow. */
+START_TEST(test_replay_overflow)
+{
+    static uint8_t  buf[LINK_MTU + 256];
+    uint8_t         ref[64];
+    uint32_t        frame_len, i;
+    uint16_t        ip_len;
+    int             ret;
+    wolfIP_esp_sa * esp_sa = NULL;
+    struct wolfIP_ip_packet *ip = (struct wolfIP_ip_packet *)buf;
+
+    for (i = 0U; i < sizeof(ref); i++) ref[i] = (uint8_t)(i & 0xFFU);
+
+    esp_setup();
+
+    ret = wolfIP_esp_sa_new_gcm(0, (uint8_t *)spi_rt,
+                                atoip4(T_SRC), atoip4(T_DST),
+                                ESP_ENC_GCM_RFC4543,
+                                (uint8_t *)k_aes256_gcm,
+                                sizeof(k_aes256_gcm));
+    ck_assert_int_eq(ret, 0);
+    esp_sa = esp_sa_get(0, (uint8_t *)spi_rt);
+    ck_assert_ptr_nonnull(esp_sa);
+
+    /* Set oseq to 10 before overflow. */
+    esp_sa->replay.oseq = (ESP_MAX_32_SEQ - 10);
+
+    /* all of these should be ok. */
+    for (i = 0; i < 10; ++i) {
+        frame_len = build_ip_packet(buf, sizeof(buf), WI_IPPROTO_UDP,
+                                    ref, sizeof(ref));
+        ip_len    = (uint16_t)(frame_len - ETH_HEADER_LEN);
+
+        ret = esp_transport_wrap(ip, &ip_len);
+        ck_assert_int_eq(ret, 0);
+    }
+
+    /* all of these should be rejected, oseq overflow is detected. */
+    for (i = 0; i < 10; ++i) {
+        frame_len = build_ip_packet(buf, sizeof(buf), WI_IPPROTO_UDP,
+                                    ref, sizeof(ref));
+        ip_len    = (uint16_t)(frame_len - ETH_HEADER_LEN);
+
+        ret = esp_transport_wrap(ip, &ip_len);
+        ck_assert_int_eq(ret, -1);
+    }
+}
+END_TEST
+
 /*
  * esp_transport_unwrap error paths
  */
@@ -1123,6 +1172,7 @@ static Suite *esp_suite(void)
     tcase_add_test(tc, test_replay_low_hi_seq_accepts_seq_one);
     tcase_add_test(tc, test_replay_jump_resets_bitmap);
     tcase_add_test(tc, test_replay_old_seqs_after_jump);
+    tcase_add_test(tc, test_replay_overflow);
     suite_add_tcase(s, tc);
 
     /* Unwrap error paths */
diff --git a/src/wolfesp.c b/src/wolfesp.c
index 003884f..4ada1d7 100644
--- a/src/wolfesp.c
+++ b/src/wolfesp.c
@@ -1489,10 +1489,15 @@ esp_transport_wrap(struct wolfIP_ip_packet *ip, uint16_t * ip_len)
     memcpy(payload, esp_sa->spi, sizeof(esp_sa->spi));
     payload += ESP_SPI_LEN;
 
+    esp_sa->replay.oseq++;
+    if (esp_sa->replay.oseq == 0) {
+        esp_sa->replay.oseq--;
+        ESP_LOG("error: oseq overflow\n");
+        return -1;
+    }
     seq_n = ee32(esp_sa->replay.oseq);
     memcpy(payload, &seq_n, sizeof(seq_n));
     payload += ESP_SEQ_LEN;
-    esp_sa->replay.oseq++;
 
     if (iv_len) {
         /* skip iv field, will generate later. */
diff --git a/wolfesp.h b/wolfesp.h
index e0c7823..a2101cf 100644
--- a/wolfesp.h
+++ b/wolfesp.h
@@ -69,7 +69,7 @@ typedef struct replay_t replay_t;
     do {                             \
         (r).bitmap = 0U;             \
         (r).hi_seq = ESP_REPLAY_WIN; \
-        (r).oseq = 1U;               \
+        (r).oseq = 0U;               \
     } while (0)
 
 /* Minimal ESP Security Association structure.