diff --git a/c/src/transport_kcp.c b/c/src/transport_kcp.c
index 9614e06..c1e2aab 100644
--- a/c/src/transport_kcp.c
+++ b/c/src/transport_kcp.c
@@ -1541,6 +1541,7 @@ int kcp_conn_send(kcp_conn_t *conn, const message_t *msg) {
     uint8_t *frame = NULL;
     size_t frame_len = 0;
     int send_errno = 0;
+    int kcp_send_rc = 0;
     if (conn == NULL || msg == NULL) {
         errno = EINVAL;
         return -1;
@@ -1554,9 +1555,10 @@ int kcp_conn_send(kcp_conn_t *conn, const message_t *msg) {
     pthread_mutex_lock(&conn->kcp_mu);
     atomic_store(&conn->sock_state->last_send_errno, 0);
     conn->kcp->current = omni_now_millis32();
-    if (ikcp_send(conn->kcp, (const char *) frame, (int) frame_len) != 0) {
+    kcp_send_rc = ikcp_send(conn->kcp, (const char *) frame, (int) frame_len);
+    if (kcp_send_rc < 0) {
         pthread_mutex_unlock(&conn->kcp_mu);
-        errno = EIO;
+        errno = kcp_send_rc == -2 ? EMSGSIZE : EINVAL;
         free(frame);
         return -1;
     }