diff --git a/mongoose.c b/mongoose.c
index 44539e818c..d1dc1139d5 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -4108,6 +4108,8 @@ struct connstate {
 #define MIP_TTYPE_FIN 4  // FIN sent, waiting until terminating the connection
   uint8_t tmiss;         // Number of keep-alive misses
   struct mg_iobuf raw;   // For TLS only. Incoming raw data
+  bool fin_sent;         // We have sent FIN to the peer
+  bool fin_rcvd;         // We have received FIN from the peer
 };
 
 #pragma pack(push, 1)
@@ -4722,7 +4724,7 @@ long mg_io_send(struct mg_connection *c, const void *buf, size_t len) {
 }
 
 static void handle_tls_recv(struct mg_connection *c) {
-  size_t avail = mg_tls_pending(c); 
+  size_t avail = mg_tls_pending(c);
   size_t min = avail > MG_MAX_RECV_SIZE ? MG_MAX_RECV_SIZE : avail;
   struct mg_iobuf *io = &c->recv;
   if (io->size - io->len < min && !mg_iobuf_resize(io, io->len + min)) {
@@ -4736,7 +4738,7 @@ static void handle_tls_recv(struct mg_connection *c) {
       // Decrypted successfully - trigger MG_EV_READ
       io->len += (size_t) n;
       mg_call(c, MG_EV_READ, &n);
-    } // else n < 0: outstanding data to be moved to c->recv
+    }  // else n < 0: outstanding data to be moved to c->recv
   }
 }
 
@@ -4752,21 +4754,28 @@ static void read_conn(struct mg_connection *c, struct pkt *pkt) {
     // closure process
     uint8_t flags = TH_ACK;
     s->ack = (uint32_t) (mg_htonl(pkt->tcp->seq) + pkt->pay.len + 1);
+    s->fin_rcvd = true;
     if (c->is_draining && s->ttype == MIP_TTYPE_FIN) {
       if (s->seq == mg_htonl(pkt->tcp->ack)) {  // Simultaneous closure ?
         s->seq++;                               // Yes. Increment our SEQ
       } else {                                  // Otherwise,
         s->seq = mg_htonl(pkt->tcp->ack);       // Set to peer's ACK
       }
+      if (s->fin_sent) c->is_closing = 1;  // Both sides closed, we're done
     } else {
       flags |= TH_FIN;
       c->is_draining = 1;
+      s->fin_sent = true;
       settmout(c, MIP_TTYPE_FIN);
     }
     tx_tcp(c->mgr->ifp, s->mac, rem_ip, flags, c->loc.port, c->rem.port,
            mg_htonl(s->seq), mg_htonl(s->ack), "", 0);
   } else if (pkt->pay.len == 0) {
-    // TODO(cpq): handle this peer's ACK
+    // If we receive a final ACK in TCP closure, close immediately,
+    // don't wait until MIP_TTYPE_FIN timeout expires
+    if (s->fin_rcvd && s->fin_sent) {
+      c->is_closing = true;
+    }
   } else if (seq != s->ack) {
     uint32_t ack = (uint32_t) (mg_htonl(pkt->tcp->seq) + pkt->pay.len);
     if (s->ack == ack) {
@@ -5213,6 +5222,7 @@ static void init_closure(struct mg_connection *c) {
     tx_tcp(c->mgr->ifp, s->mac, rem_ip, TH_FIN | TH_ACK, c->loc.port,
            c->rem.port, mg_htonl(s->seq), mg_htonl(s->ack), NULL, 0);
     settmout(c, MIP_TTYPE_FIN);
+    s->fin_sent = true;
   }
 }
 
diff --git a/src/net_builtin.c b/src/net_builtin.c
index 57b4017675..94201a830f 100644
--- a/src/net_builtin.c
+++ b/src/net_builtin.c
@@ -28,6 +28,8 @@ struct connstate {
 #define MIP_TTYPE_FIN 4  // FIN sent, waiting until terminating the connection
   uint8_t tmiss;         // Number of keep-alive misses
   struct mg_iobuf raw;   // For TLS only. Incoming raw data
+  bool fin_sent;         // We have sent FIN to the peer
+  bool fin_rcvd;         // We have received FIN from the peer
 };
 
 #pragma pack(push, 1)
@@ -642,7 +644,7 @@ long mg_io_send(struct mg_connection *c, const void *buf, size_t len) {
 }
 
 static void handle_tls_recv(struct mg_connection *c) {
-  size_t avail = mg_tls_pending(c); 
+  size_t avail = mg_tls_pending(c);
   size_t min = avail > MG_MAX_RECV_SIZE ? MG_MAX_RECV_SIZE : avail;
   struct mg_iobuf *io = &c->recv;
   if (io->size - io->len < min && !mg_iobuf_resize(io, io->len + min)) {
@@ -656,7 +658,7 @@ static void handle_tls_recv(struct mg_connection *c) {
       // Decrypted successfully - trigger MG_EV_READ
       io->len += (size_t) n;
       mg_call(c, MG_EV_READ, &n);
-    } // else n < 0: outstanding data to be moved to c->recv
+    }  // else n < 0: outstanding data to be moved to c->recv
   }
 }
 
@@ -672,21 +674,28 @@ static void read_conn(struct mg_connection *c, struct pkt *pkt) {
     // closure process
     uint8_t flags = TH_ACK;
     s->ack = (uint32_t) (mg_htonl(pkt->tcp->seq) + pkt->pay.len + 1);
+    s->fin_rcvd = true;
     if (c->is_draining && s->ttype == MIP_TTYPE_FIN) {
       if (s->seq == mg_htonl(pkt->tcp->ack)) {  // Simultaneous closure ?
         s->seq++;                               // Yes. Increment our SEQ
       } else {                                  // Otherwise,
         s->seq = mg_htonl(pkt->tcp->ack);       // Set to peer's ACK
       }
+      if (s->fin_sent) c->is_closing = 1;  // Both sides closed, we're done
     } else {
       flags |= TH_FIN;
       c->is_draining = 1;
+      s->fin_sent = true;
       settmout(c, MIP_TTYPE_FIN);
     }
     tx_tcp(c->mgr->ifp, s->mac, rem_ip, flags, c->loc.port, c->rem.port,
            mg_htonl(s->seq), mg_htonl(s->ack), "", 0);
   } else if (pkt->pay.len == 0) {
-    // TODO(cpq): handle this peer's ACK
+    // If we receive a final ACK in TCP closure, close immediately,
+    // don't wait until MIP_TTYPE_FIN timeout expires
+    if (s->fin_rcvd && s->fin_sent) {
+      c->is_closing = true;
+    }
   } else if (seq != s->ack) {
     uint32_t ack = (uint32_t) (mg_htonl(pkt->tcp->seq) + pkt->pay.len);
     if (s->ack == ack) {
@@ -1133,6 +1142,7 @@ static void init_closure(struct mg_connection *c) {
     tx_tcp(c->mgr->ifp, s->mac, rem_ip, TH_FIN | TH_ACK, c->loc.port,
            c->rem.port, mg_htonl(s->seq), mg_htonl(s->ack), NULL, 0);
     settmout(c, MIP_TTYPE_FIN);
+    s->fin_sent = true;
   }
 }