diff --git a/src/core/tcp_out.c b/src/core/tcp_out.c
index 1f42eeda..95065834 100644
--- a/src/core/tcp_out.c
+++ b/src/core/tcp_out.c
@@ -835,9 +835,9 @@ tcp_enqueue_flags(struct tcp_pcb *pcb, u8_t flags)
 #endif /* LWIP_WND_SCALE */
   }
 #if LWIP_TCP_TIMESTAMPS
-  if ((pcb->flags & TF_TIMESTAMP)) {
-    /* Make sure the timestamp option is only included in data segments if we
-       agreed about it with the remote host. */
+  if ((pcb->flags & TF_TIMESTAMP) || ((flags & TCP_SYN) && (pcb->state != SYN_RCVD))) {
+    /* The timestamp option is only included in SYN packets,
+     * and in data segments if we agreed about it with the remote host. */
     optflags |= TF_SEG_OPTS_TS;
   }
 #endif /* LWIP_TCP_TIMESTAMPS */