diff --git a/CHANGELOG b/CHANGELOG
index c217efb9..f3015a80 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -100,6 +100,10 @@ HISTORY
 
  ++ Bugfixes:
 
+  2014-04-06: Simon Goldschmidt
+  * tcp_in.c: Fixed bug #36210 lwIP does not elicit an empty ACK when received
+    unacceptable ACK
+
   2014-04-06: Simon Goldschmidt
   * dhcp.c, ip4.c/.h, ip6.c/.h, udp.c/.h, ip.h: Fixed bug #41787 DHCP Discovery
     is invalid when an IP is set to thet netif.
diff --git a/src/core/tcp_in.c b/src/core/tcp_in.c
index bf921a84..d3b8a126 100644
--- a/src/core/tcp_in.c
+++ b/src/core/tcp_in.c
@@ -1112,8 +1112,9 @@ tcp_receive(struct tcp_pcb *pcb)
       }
 #endif /* LWIP_IPV6 && LWIP_ND6_TCP_REACHABILITY_HINTS*/
     } else {
-      /* Fix bug bug #21582: out of sequence ACK, didn't really ack anything */
+      /* Out of sequence ACK, didn't really ack anything */
       pcb->acked = 0;
+      tcp_send_empty_ack(pcb);
     }
 
     /* We go through the ->unsent list to see if any of the segments