diff --git a/cproxy.c b/cproxy.c
index e1d788b6..d187ffec 100644
--- a/cproxy.c
+++ b/cproxy.c
@@ -67,13 +67,13 @@ int proxy_socks5_handlechap (ProxySocket *p)
             if (data[0] != 0x01) {
                 plug_closing(p->plug, "Proxy error: SOCKS proxy wants"
                              " a different CHAP version",
-                             PROXY_ERROR_GENERAL, 0);
+                             PROXY_ERROR_GENERAL);
                 return 1;
             }
             if (data[1] == 0x00) {
                 plug_closing(p->plug, "Proxy error: SOCKS proxy won't"
                              " negotiate CHAP with us",
-                             PROXY_ERROR_GENERAL, 0);
+                             PROXY_ERROR_GENERAL);
                 return 1;
             }
             p->chap_num_attributes = data[1];
@@ -105,7 +105,7 @@ int proxy_socks5_handlechap (ProxySocket *p)
                 else {
                     plug_closing(p->plug, "Proxy error: SOCKS proxy"
                                  " refused CHAP authentication",
-                                 PROXY_ERROR_GENERAL, 0);
+                                 PROXY_ERROR_GENERAL);
                     return 1;
                 }
               break;
@@ -125,7 +125,7 @@ int proxy_socks5_handlechap (ProxySocket *p)
                     plug_closing(p->plug, "Proxy error: Server chose "
                                  "CHAP of other than HMAC-MD5 but we "
                                  "didn't offer it!",
-                                 PROXY_ERROR_GENERAL, 0);
+                                 PROXY_ERROR_GENERAL);
                     return 1;
                 }
               break;
@@ -174,6 +174,6 @@ int proxy_socks5_selectchap(ProxySocket *p)
     } else
         plug_closing(p->plug, "Proxy error: Server chose "
                      "CHAP authentication but we didn't offer it!",
-                 PROXY_ERROR_GENERAL, 0);
+                     PROXY_ERROR_GENERAL);
     return 1;
 }
diff --git a/network.h b/network.h
index 85c5a6d9..ff88923b 100644
--- a/network.h
+++ b/network.h
@@ -87,7 +87,7 @@ struct PlugVtable {
      * the logged events.
      */
     void (*closing)
-     (Plug *p, const char *error_msg, int error_code, bool calling_back);
+     (Plug *p, const char *error_msg, int error_code);
     /* error_msg is NULL iff it is not an error (ie it closed normally) */
     /* calling_back != 0 iff there is a Plug function */
     /* currently running (would cure the fixme in try_send()) */
@@ -214,9 +214,8 @@ static inline void sk_write_eof(Socket *s)
 static inline void plug_log(
     Plug *p, int type, SockAddr *addr, int port, const char *msg, int code)
 { p->vt->log(p, type, addr, port, msg, code); }
-static inline void plug_closing(
-    Plug *p, const char *msg, int code, bool calling_back)
-{ p->vt->closing(p, msg, code, calling_back); }
+static inline void plug_closing(Plug *p, const char *msg, int code)
+{ p->vt->closing(p, msg, code); }
 static inline void plug_receive(Plug *p, int urg, const char *data, size_t len)
 { p->vt->receive(p, urg, data, len); }
 static inline void plug_sent (Plug *p, size_t bufsize)
@@ -341,8 +340,7 @@ extern Plug *const nullplug;
  */
 void nullplug_log(Plug *plug, PlugLogType type, SockAddr *addr,
                   int port, const char *err_msg, int err_code);
-void nullplug_closing(Plug *plug, const char *error_msg, int error_code,
-                      bool calling_back);
+void nullplug_closing(Plug *plug, const char *error_msg, int error_code);
 void nullplug_receive(Plug *plug, int urgent, const char *data, size_t len);
 void nullplug_sent(Plug *plug, size_t bufsize);
 
diff --git a/nocproxy.c b/nocproxy.c
index f93214fa..cdc28a39 100644
--- a/nocproxy.c
+++ b/nocproxy.c
@@ -22,7 +22,7 @@ int proxy_socks5_handlechap (ProxySocket *p)
 
     plug_closing(p->plug, "Proxy error: Trying to handle a SOCKS5 CHAP request"
                  " in telnet-only build",
-                 PROXY_ERROR_GENERAL, 0);
+                 PROXY_ERROR_GENERAL);
     return 1;
 }
 
@@ -30,6 +30,6 @@ int proxy_socks5_selectchap(ProxySocket *p)
 {
     plug_closing(p->plug, "Proxy error: Trying to handle a SOCKS5 CHAP request"
                  " in telnet-only build",
-                 PROXY_ERROR_GENERAL, 0);
+                 PROXY_ERROR_GENERAL);
     return 1;
 }
diff --git a/nullplug.c b/nullplug.c
index 380e4b4f..ad65f5ea 100644
--- a/nullplug.c
+++ b/nullplug.c
@@ -12,8 +12,7 @@ void nullplug_log(Plug *plug, PlugLogType type, SockAddr *addr,
 {
 }
 
-void nullplug_closing(Plug *plug, const char *error_msg, int error_code,
-                      bool calling_back)
+void nullplug_closing(Plug *plug, const char *error_msg, int error_code)
 {
 }
 
diff --git a/otherbackends/raw.c b/otherbackends/raw.c
index 97b7be09..491a3df9 100644
--- a/otherbackends/raw.c
+++ b/otherbackends/raw.c
@@ -69,8 +69,7 @@ static void raw_check_close(Raw *raw)
     }
 }
 
-static void raw_closing(Plug *plug, const char *error_msg, int error_code,
-                        bool calling_back)
+static void raw_closing(Plug *plug, const char *error_msg, int error_code)
 {
     Raw *raw = container_of(plug, Raw, plug);
 
diff --git a/otherbackends/rlogin.c b/otherbackends/rlogin.c
index 09f1ab1d..9951ce18 100644
--- a/otherbackends/rlogin.c
+++ b/otherbackends/rlogin.c
@@ -89,8 +89,7 @@ static void rlogin_log(Plug *plug, PlugLogType type, SockAddr *addr, int port,
     }
 }
 
-static void rlogin_closing(Plug *plug, const char *error_msg, int error_code,
-                           bool calling_back)
+static void rlogin_closing(Plug *plug, const char *error_msg, int error_code)
 {
     Rlogin *rlogin = container_of(plug, Rlogin, plug);
 
diff --git a/otherbackends/supdup.c b/otherbackends/supdup.c
index a3418fe1..f015e054 100644
--- a/otherbackends/supdup.c
+++ b/otherbackends/supdup.c
@@ -577,8 +577,7 @@ static void supdup_log(Plug *plug, PlugLogType type, SockAddr *addr, int port,
     }
 }
 
-static void supdup_closing(Plug *plug, const char *error_msg, int error_code,
-                           bool calling_back)
+static void supdup_closing(Plug *plug, const char *error_msg, int error_code)
 {
     Supdup *supdup = container_of(plug, Supdup, plug);
 
diff --git a/otherbackends/telnet.c b/otherbackends/telnet.c
index 98c202c6..281c39ac 100644
--- a/otherbackends/telnet.c
+++ b/otherbackends/telnet.c
@@ -639,8 +639,7 @@ static void telnet_log(Plug *plug, PlugLogType type, SockAddr *addr, int port,
     }
 }
 
-static void telnet_closing(Plug *plug, const char *error_msg, int error_code,
-                           bool calling_back)
+static void telnet_closing(Plug *plug, const char *error_msg, int error_code)
 {
     Telnet *telnet = container_of(plug, Telnet, plug);
 
diff --git a/pageant.c b/pageant.c
index 89256b53..bb658cfe 100644
--- a/pageant.c
+++ b/pageant.c
@@ -1464,7 +1464,7 @@ struct pageant_conn_state {
 };
 
 static void pageant_conn_closing(Plug *plug, const char *error_msg,
-                                 int error_code, bool calling_back)
+                                 int error_code)
 {
     struct pageant_conn_state *pc = container_of(
         plug, struct pageant_conn_state, plug);
@@ -1611,7 +1611,7 @@ struct pageant_listen_state {
 };
 
 static void pageant_listen_closing(Plug *plug, const char *error_msg,
-                                   int error_code, bool calling_back)
+                                   int error_code)
 {
     struct pageant_listen_state *pl = container_of(
         plug, struct pageant_listen_state, plug);
diff --git a/proxy.c b/proxy.c
index 97a4b1df..08d5afba 100644
--- a/proxy.c
+++ b/proxy.c
@@ -181,18 +181,16 @@ static void plug_proxy_log(Plug *plug, PlugLogType type, SockAddr *addr,
     plug_log(ps->plug, type, addr, port, error_msg, error_code);
 }
 
-static void plug_proxy_closing (Plug *p, const char *error_msg,
-                                int error_code, bool calling_back)
+static void plug_proxy_closing(Plug *p, const char *error_msg, int error_code)
 {
     ProxySocket *ps = container_of(p, ProxySocket, plugimpl);
 
     if (ps->state != PROXY_STATE_ACTIVE) {
         ps->closing_error_msg = error_msg;
         ps->closing_error_code = error_code;
-        ps->closing_calling_back = calling_back;
         ps->negotiate(ps, PROXY_CHANGE_CLOSING);
     } else {
-        plug_closing(ps->plug, error_msg, error_code, calling_back);
+        plug_closing(ps->plug, error_msg, error_code);
     }
 }
 
@@ -617,8 +615,7 @@ int proxy_http_negotiate (ProxySocket *p, int change)
          * a socket close, then some error must have occurred. we'll
          * just pass those errors up to the backend.
          */
-        plug_closing(p->plug, p->closing_error_msg, p->closing_error_code,
-                     p->closing_calling_back);
+        plug_closing(p->plug, p->closing_error_msg, p->closing_error_code);
         return 0; /* ignored */
     }
 
@@ -675,7 +672,7 @@ int proxy_http_negotiate (ProxySocket *p, int change)
             if (sscanf((char *)data, "HTTP/%i.%i %n",
                        &maj_ver, &min_ver, &status) < 2 || status == -1) {
                 plug_closing(p->plug, "Proxy error: HTTP response was absent",
-                             PROXY_ERROR_GENERAL, 0);
+                             PROXY_ERROR_GENERAL);
                 sfree(data);
                 return 1;
             }
@@ -690,7 +687,7 @@ int proxy_http_negotiate (ProxySocket *p, int change)
                        (data[eol-1] == '\r' || data[eol-1] == '\n'))
                     data[--eol] = '\0';
                 buf = dupprintf("Proxy error: %s", data+status);
-                plug_closing(p->plug, buf, PROXY_ERROR_GENERAL, 0);
+                plug_closing(p->plug, buf, PROXY_ERROR_GENERAL);
                 sfree(buf);
                 sfree(data);
                 return 1;
@@ -741,7 +738,7 @@ int proxy_http_negotiate (ProxySocket *p, int change)
     }
 
     plug_closing(p->plug, "Proxy error: unexpected proxy error",
-                 PROXY_ERROR_UNEXPECTED, 0);
+                 PROXY_ERROR_UNEXPECTED);
     return 1;
 }
 
@@ -807,8 +804,7 @@ int proxy_socks4_negotiate (ProxySocket *p, int change)
          * a socket close, then some error must have occurred. we'll
          * just pass those errors up to the backend.
          */
-        plug_closing(p->plug, p->closing_error_msg, p->closing_error_code,
-                     p->closing_calling_back);
+        plug_closing(p->plug, p->closing_error_msg, p->closing_error_code);
         return 0; /* ignored */
     }
 
@@ -860,7 +856,7 @@ int proxy_socks4_negotiate (ProxySocket *p, int change)
             if (data[0] != 0) {
                 plug_closing(p->plug, "Proxy error: SOCKS proxy responded with "
                                       "unexpected reply code version",
-                             PROXY_ERROR_GENERAL, 0);
+                             PROXY_ERROR_GENERAL);
                 return 1;
             }
 
@@ -869,16 +865,16 @@ int proxy_socks4_negotiate (ProxySocket *p, int change)
                 switch (data[1]) {
                   case 92:
                     plug_closing(p->plug, "Proxy error: SOCKS server wanted IDENTD on client",
-                                 PROXY_ERROR_GENERAL, 0);
+                                 PROXY_ERROR_GENERAL);
                     break;
                   case 93:
                     plug_closing(p->plug, "Proxy error: Username and IDENTD on client don't agree",
-                                 PROXY_ERROR_GENERAL, 0);
+                                 PROXY_ERROR_GENERAL);
                     break;
                   case 91:
                   default:
                     plug_closing(p->plug, "Proxy error: Error while communicating with proxy",
-                                 PROXY_ERROR_GENERAL, 0);
+                                 PROXY_ERROR_GENERAL);
                     break;
                 }
 
@@ -895,7 +891,7 @@ int proxy_socks4_negotiate (ProxySocket *p, int change)
     }
 
     plug_closing(p->plug, "Proxy error: unexpected proxy error",
-                 PROXY_ERROR_UNEXPECTED, 0);
+                 PROXY_ERROR_UNEXPECTED);
     return 1;
 }
 
@@ -951,8 +947,7 @@ int proxy_socks5_negotiate (ProxySocket *p, int change)
          * a socket close, then some error must have occurred. we'll
          * just pass those errors up to the backend.
          */
-        plug_closing(p->plug, p->closing_error_msg, p->closing_error_code,
-                     p->closing_calling_back);
+        plug_closing(p->plug, p->closing_error_msg, p->closing_error_code);
         return 0; /* ignored */
     }
 
@@ -1002,7 +997,7 @@ int proxy_socks5_negotiate (ProxySocket *p, int change)
 
             if (data[0] != 5) {
                 plug_closing(p->plug, "Proxy error: SOCKS proxy returned unexpected version",
-                             PROXY_ERROR_GENERAL, 0);
+                             PROXY_ERROR_GENERAL);
                 return 1;
             }
 
@@ -1012,7 +1007,7 @@ int proxy_socks5_negotiate (ProxySocket *p, int change)
             else if (data[1] == 0x03) p->state = 6; /* CHAP authentication */
             else {
                 plug_closing(p->plug, "Proxy error: SOCKS proxy did not accept our authentication",
-                             PROXY_ERROR_GENERAL, 0);
+                             PROXY_ERROR_GENERAL);
                 return 1;
             }
             bufchain_consume(&p->pending_input_data, 2);
@@ -1037,7 +1032,7 @@ int proxy_socks5_negotiate (ProxySocket *p, int change)
             if (data[0] != 1) {
                 plug_closing(p->plug, "Proxy error: SOCKS password "
                              "subnegotiation contained wrong version number",
-                             PROXY_ERROR_GENERAL, 0);
+                             PROXY_ERROR_GENERAL);
                 return 1;
             }
 
@@ -1045,7 +1040,7 @@ int proxy_socks5_negotiate (ProxySocket *p, int change)
 
                 plug_closing(p->plug, "Proxy error: SOCKS proxy refused"
                              " password authentication",
-                             PROXY_ERROR_GENERAL, 0);
+                             PROXY_ERROR_GENERAL);
                 return 1;
             }
 
@@ -1148,7 +1143,7 @@ int proxy_socks5_negotiate (ProxySocket *p, int change)
 
             if (data[0] != 5) {
                 plug_closing(p->plug, "Proxy error: SOCKS proxy returned wrong version number",
-                             PROXY_ERROR_GENERAL, 0);
+                             PROXY_ERROR_GENERAL);
                 return 1;
             }
 
@@ -1171,7 +1166,7 @@ int proxy_socks5_negotiate (ProxySocket *p, int change)
                                    data[1]);
                     break;
                 }
-                plug_closing(p->plug, buf, PROXY_ERROR_GENERAL, 0);
+                plug_closing(p->plug, buf, PROXY_ERROR_GENERAL);
 
                 return 1;
             }
@@ -1187,7 +1182,7 @@ int proxy_socks5_negotiate (ProxySocket *p, int change)
               default:
                 plug_closing(p->plug, "Proxy error: SOCKS proxy returned "
                              "unrecognised address format",
-                             PROXY_ERROR_GENERAL, 0);
+                             PROXY_ERROR_GENERAL);
                 return 1;
             }
             if (bufchain_size(&p->pending_input_data) < len)
@@ -1202,7 +1197,7 @@ int proxy_socks5_negotiate (ProxySocket *p, int change)
         if (p->state == 4) {
             /* TODO: Handle GSSAPI authentication */
             plug_closing(p->plug, "Proxy error: We don't support GSSAPI authentication",
-                         PROXY_ERROR_GENERAL, 0);
+                         PROXY_ERROR_GENERAL);
             return 1;
         }
 
@@ -1231,7 +1226,7 @@ int proxy_socks5_negotiate (ProxySocket *p, int change)
                 plug_closing(p->plug, "Proxy error: Server chose "
                              "username/password authentication but we "
                              "didn't offer it!",
-                         PROXY_ERROR_GENERAL, 0);
+                             PROXY_ERROR_GENERAL);
             return 1;
         }
 
@@ -1244,7 +1239,7 @@ int proxy_socks5_negotiate (ProxySocket *p, int change)
     }
 
     plug_closing(p->plug, "Proxy error: Unexpected proxy error",
-                 PROXY_ERROR_UNEXPECTED, 0);
+                 PROXY_ERROR_UNEXPECTED);
     return 1;
 }
 
@@ -1479,8 +1474,7 @@ int proxy_telnet_negotiate (ProxySocket *p, int change)
          * a socket close, then some error must have occurred. we'll
          * just pass those errors up to the backend.
          */
-        plug_closing(p->plug, p->closing_error_msg, p->closing_error_code,
-                     p->closing_calling_back);
+        plug_closing(p->plug, p->closing_error_msg, p->closing_error_code);
         return 0; /* ignored */
     }
 
@@ -1516,6 +1510,6 @@ int proxy_telnet_negotiate (ProxySocket *p, int change)
     }
 
     plug_closing(p->plug, "Proxy error: Unexpected proxy error",
-                 PROXY_ERROR_UNEXPECTED, 0);
+                 PROXY_ERROR_UNEXPECTED);
     return 1;
 }
diff --git a/proxy.h b/proxy.h
index f11e1e3d..9dca87d1 100644
--- a/proxy.h
+++ b/proxy.h
@@ -63,7 +63,6 @@ struct ProxySocket {
     /* closing */
     const char *closing_error_msg;
     int closing_error_code;
-    bool closing_calling_back;
 
     /* receive */
     bool receive_urgent;
diff --git a/psocks.c b/psocks.c
index 75dc85d9..50bdf714 100644
--- a/psocks.c
+++ b/psocks.c
@@ -95,7 +95,7 @@ static const SshChannelVtable psocks_scvt = {
 static void psocks_plug_log(Plug *p, PlugLogType type, SockAddr *addr,
                             int port, const char *error_msg, int error_code);
 static void psocks_plug_closing(Plug *p, const char *error_msg,
-                                int error_code, bool calling_back);
+                                int error_code);
 static void psocks_plug_receive(Plug *p, int urgent,
                                 const char *data, size_t len);
 static void psocks_plug_sent(Plug *p, size_t bufsize);
@@ -355,7 +355,7 @@ static void psocks_plug_log(Plug *plug, PlugLogType type, SockAddr *addr,
 }
 
 static void psocks_plug_closing(Plug *plug, const char *error_msg,
-                                int error_code, bool calling_back)
+                                int error_code)
 {
     psocks_connection *conn = container_of(plug, psocks_connection, plug);
     if (conn->connecting) {
diff --git a/ssh/portfwd.c b/ssh/portfwd.c
index 268935eb..9dd35ea4 100644
--- a/ssh/portfwd.c
+++ b/ssh/portfwd.c
@@ -109,8 +109,7 @@ static void pfl_log(Plug *plug, PlugLogType type, SockAddr *addr, int port,
 
 static void pfd_close(struct PortForwarding *pf);
 
-static void pfd_closing(Plug *plug, const char *error_msg, int error_code,
-                        bool calling_back)
+static void pfd_closing(Plug *plug, const char *error_msg, int error_code)
 {
     struct PortForwarding *pf =
         container_of(plug, struct PortForwarding, plug);
@@ -142,8 +141,7 @@ static void pfd_closing(Plug *plug, const char *error_msg, int error_code,
 
 static void pfl_terminate(struct PortListener *pl);
 
-static void pfl_closing(Plug *plug, const char *error_msg, int error_code,
-                        bool calling_back)
+static void pfl_closing(Plug *plug, const char *error_msg, int error_code)
 {
     struct PortListener *pl = (struct PortListener *) plug;
     pfl_terminate(pl);
diff --git a/ssh/server.c b/ssh/server.c
index 4a3676ec..404ba77d 100644
--- a/ssh/server.c
+++ b/ssh/server.c
@@ -139,8 +139,7 @@ static void server_socket_log(Plug *plug, PlugLogType type, SockAddr *addr,
     /* FIXME */
 }
 
-static void server_closing(Plug *plug, const char *error_msg, int error_code,
-                           bool calling_back)
+static void server_closing(Plug *plug, const char *error_msg, int error_code)
 {
     server *srv = container_of(plug, server, plug);
     if (error_msg) {
diff --git a/ssh/sesschan.c b/ssh/sesschan.c
index 1ef55dde..ff4a008f 100644
--- a/ssh/sesschan.c
+++ b/ssh/sesschan.c
@@ -366,8 +366,7 @@ bool sesschan_run_subsystem(Channel *chan, ptrlen subsys)
 static void fwd_log(Plug *plug, PlugLogType type, SockAddr *addr, int port,
                     const char *error_msg, int error_code)
 { /* don't expect any weirdnesses from a listening socket */ }
-static void fwd_closing(Plug *plug, const char *error_msg, int error_code,
-                        bool calling_back)
+static void fwd_closing(Plug *plug, const char *error_msg, int error_code)
 { /* not here, either */ }
 
 static int xfwd_accepting(Plug *p, accept_fn_t constructor, accept_ctx_t ctx)
diff --git a/ssh/sharing.c b/ssh/sharing.c
index 920218de..92e2a786 100644
--- a/ssh/sharing.c
+++ b/ssh/sharing.c
@@ -937,8 +937,7 @@ static void share_disconnect(struct ssh_sharing_connstate *cs,
     share_begin_cleanup(cs);
 }
 
-static void share_closing(Plug *plug, const char *error_msg, int error_code,
-                          bool calling_back)
+static void share_closing(Plug *plug, const char *error_msg, int error_code)
 {
     struct ssh_sharing_connstate *cs = container_of(
         plug, struct ssh_sharing_connstate, plug);
@@ -1846,7 +1845,7 @@ static void share_sent(Plug *plug, size_t bufsize)
 }
 
 static void share_listen_closing(Plug *plug, const char *error_msg,
-                                 int error_code, bool calling_back)
+                                 int error_code)
 {
     ssh_sharing_state *sharestate =
         container_of(plug, ssh_sharing_state, plug);
diff --git a/ssh/ssh.c b/ssh/ssh.c
index 4e7f8c06..b2d75b09 100644
--- a/ssh/ssh.c
+++ b/ssh/ssh.c
@@ -609,8 +609,7 @@ static void ssh_socket_log(Plug *plug, PlugLogType type, SockAddr *addr,
     }
 }
 
-static void ssh_closing(Plug *plug, const char *error_msg, int error_code,
-                        bool calling_back)
+static void ssh_closing(Plug *plug, const char *error_msg, int error_code)
 {
     Ssh *ssh = container_of(plug, Ssh, plug);
     if (error_msg) {
diff --git a/ssh/x11fwd.c b/ssh/x11fwd.c
index 60a9f1aa..6886dace 100644
--- a/ssh/x11fwd.c
+++ b/ssh/x11fwd.c
@@ -267,8 +267,7 @@ static void x11_log(Plug *p, PlugLogType type, SockAddr *addr, int port,
 static void x11_send_init_error(struct X11Connection *conn,
                                 const char *err_message);
 
-static void x11_closing(Plug *plug, const char *error_msg, int error_code,
-                        bool calling_back)
+static void x11_closing(Plug *plug, const char *error_msg, int error_code)
 {
     struct X11Connection *xconn = container_of(
         plug, struct X11Connection, plug);
diff --git a/sshproxy.c b/sshproxy.c
index aea19cf6..31657645 100644
--- a/sshproxy.c
+++ b/sshproxy.c
@@ -244,7 +244,7 @@ static void try_send_ssh_to_socket(void *ctx)
     if (sp->rcvd_eof_ssh_to_socket &&
         !sp->sent_eof_ssh_to_socket) {
         sp->sent_eof_ssh_to_socket = true;
-        plug_closing(sp->plug, sp->errmsg, 0, 0);
+        plug_closing(sp->plug, sp->errmsg, 0);
     }
 }
 
@@ -325,7 +325,7 @@ static int sshproxy_get_userpass_input(Seat *seat, prompts_t *p)
 static void sshproxy_connection_fatal_callback(void *vctx)
 {
     SshProxy *sp = (SshProxy *)vctx;
-    plug_closing(sp->plug, sp->errmsg, 0, true);
+    plug_closing(sp->plug, sp->errmsg, 0);
 }
 
 static void sshproxy_connection_fatal(Seat *seat, const char *message)
diff --git a/unix/fd-socket.c b/unix/fd-socket.c
index d352d8e4..48d7dc8b 100644
--- a/unix/fd-socket.c
+++ b/unix/fd-socket.c
@@ -158,8 +158,7 @@ static void fdsocket_error_callback(void *vs)
     /*
      * An error has occurred on this socket. Pass it to the plug.
      */
-    plug_closing(fds->plug, strerror(fds->pending_error),
-                 fds->pending_error, 0);
+    plug_closing(fds->plug, strerror(fds->pending_error), fds->pending_error);
 }
 
 static int fdsocket_try_send(FdSocket *fds)
@@ -271,9 +270,9 @@ static void fdsocket_select_result_input(int fd, int event)
         fds->infd = -1;
 
         if (retd < 0) {
-            plug_closing(fds->plug, strerror(errno), errno, 0);
+            plug_closing(fds->plug, strerror(errno), errno);
         } else {
-            plug_closing(fds->plug, NULL, 0, 0);
+            plug_closing(fds->plug, NULL, 0);
         }
     }
 }
diff --git a/unix/network.c b/unix/network.c
index bd6ebb1d..d2d426ed 100644
--- a/unix/network.c
+++ b/unix/network.c
@@ -1101,7 +1101,7 @@ static void socket_error_callback(void *vs)
     /*
      * An error has occurred on this socket. Pass it to the plug.
      */
-    plug_closing(s->plug, strerror(s->pending_error), s->pending_error, 0);
+    plug_closing(s->plug, strerror(s->pending_error), s->pending_error);
 }
 
 /*
@@ -1298,7 +1298,7 @@ static void net_select_result(int fd, int event)
             if (ret <= 0) {
                 plug_closing(s->plug,
                              ret == 0 ? "Internal networking trouble" :
-                             strerror(errno), errno, 0);
+                             strerror(errno), errno);
             } else {
                 /*
                  * Receiving actual data on a socket means we can
@@ -1384,11 +1384,11 @@ static void net_select_result(int fd, int event)
             }
         }
         if (ret < 0) {
-            plug_closing(s->plug, strerror(errno), errno, 0);
+            plug_closing(s->plug, strerror(errno), errno);
         } else if (0 == ret) {
             s->incomingeof = true;     /* stop trying to read now */
             uxsel_tell(s);
-            plug_closing(s->plug, NULL, 0, 0);
+            plug_closing(s->plug, NULL, 0);
         } else {
             /*
              * Receiving actual data on a socket means we can
@@ -1438,7 +1438,7 @@ static void net_select_result(int fd, int event)
                         err = try_connect(s);
                     }
                     if (err) {
-                        plug_closing(s->plug, strerror(err), err, 0);
+                        plug_closing(s->plug, strerror(err), err);
                         return;      /* socket is now presumably defunct */
                     }
                     if (!s->connected)
diff --git a/unix/pageant.c b/unix/pageant.c
index 7402ac60..a0b2e9e2 100644
--- a/unix/pageant.c
+++ b/unix/pageant.c
@@ -249,8 +249,7 @@ static void x11_log(Plug *p, PlugLogType type, SockAddr *addr, int port,
                     const char *error_msg, int error_code) {}
 static void x11_receive(Plug *plug, int urgent, const char *data, size_t len) {}
 static void x11_sent(Plug *plug, size_t bufsize) {}
-static void x11_closing(Plug *plug, const char *error_msg, int error_code,
-                        bool calling_back)
+static void x11_closing(Plug *plug, const char *error_msg, int error_code)
 {
     time_to_die = true;
 }
diff --git a/unix/psusan.c b/unix/psusan.c
index 2017685b..8fcef33a 100644
--- a/unix/psusan.c
+++ b/unix/psusan.c
@@ -273,8 +273,7 @@ static void server_log(Plug *plug, PlugLogType type, SockAddr *addr, int port,
     log_to_stderr(-1, error_msg);
 }
 
-static void server_closing(Plug *plug, const char *error_msg, int error_code,
-                           bool calling_back)
+static void server_closing(Plug *plug, const char *error_msg, int error_code)
 {
     log_to_stderr(-1, error_msg);
 }
diff --git a/unix/uppity.c b/unix/uppity.c
index 5d0a1b1c..0701ddab 100644
--- a/unix/uppity.c
+++ b/unix/uppity.c
@@ -482,8 +482,7 @@ static void server_log(Plug *plug, PlugLogType type, SockAddr *addr, int port,
     log_to_stderr((unsigned)-1, error_msg);
 }
 
-static void server_closing(Plug *plug, const char *error_msg, int error_code,
-                           bool calling_back)
+static void server_closing(Plug *plug, const char *error_msg, int error_code)
 {
     log_to_stderr((unsigned)-1, error_msg);
 }
diff --git a/windows/handle-socket.c b/windows/handle-socket.c
index a024807e..066d2373 100644
--- a/windows/handle-socket.c
+++ b/windows/handle-socket.c
@@ -53,10 +53,10 @@ static size_t handle_gotdata(
     HandleSocket *hs = (HandleSocket *)handle_get_privdata(h);
 
     if (err) {
-        plug_closing(hs->plug, "Read error from handle", 0, 0);
+        plug_closing(hs->plug, "Read error from handle", 0);
         return 0;
     } else if (len == 0) {
-        plug_closing(hs->plug, NULL, 0, 0);
+        plug_closing(hs->plug, NULL, 0);
         return 0;
     } else {
         assert(hs->frozen != FROZEN && hs->frozen != THAWING);
@@ -107,7 +107,7 @@ static void handle_sentdata(struct handle *h, size_t new_backlog, int err,
     }
 
     if (err) {
-        plug_closing(hs->plug, win_strerror(err), err, 0);
+        plug_closing(hs->plug, win_strerror(err), err);
         return;
     }
 
diff --git a/windows/network.c b/windows/network.c
index 3b4da3cc..17c80cb4 100644
--- a/windows/network.c
+++ b/windows/network.c
@@ -1353,7 +1353,7 @@ static void socket_error_callback(void *vs)
      * An error has occurred on this socket. Pass it to the plug.
      */
     plug_closing(s->plug, winsock_error_string(s->pending_error),
-                 s->pending_error, 0);
+                 s->pending_error);
 }
 
 /*
@@ -1528,7 +1528,7 @@ void select_result(WPARAM wParam, LPARAM lParam)
             }
         }
         if (err != 0)
-            plug_closing(s->plug, winsock_error_string(err), err, 0);
+            plug_closing(s->plug, winsock_error_string(err), err);
         return;
     }
 
@@ -1590,9 +1590,9 @@ void select_result(WPARAM wParam, LPARAM lParam)
             }
         }
         if (ret < 0) {
-            plug_closing(s->plug, winsock_error_string(err), err, 0);
+            plug_closing(s->plug, winsock_error_string(err), err);
         } else if (0 == ret) {
-            plug_closing(s->plug, NULL, 0, 0);
+            plug_closing(s->plug, NULL, 0);
         } else {
             plug_receive(s->plug, atmark ? 0 : 1, buf, ret);
         }
@@ -1608,7 +1608,7 @@ void select_result(WPARAM wParam, LPARAM lParam)
         noise_ultralight(NOISE_SOURCE_IOLEN, ret);
         if (ret <= 0) {
             int err = p_WSAGetLastError();
-            plug_closing(s->plug, winsock_error_string(err), err, 0);
+            plug_closing(s->plug, winsock_error_string(err), err);
         } else {
             plug_receive(s->plug, 2, buf, ret);
         }
@@ -1631,12 +1631,12 @@ void select_result(WPARAM wParam, LPARAM lParam)
                 err = p_WSAGetLastError();
                 if (err == WSAEWOULDBLOCK)
                     break;
-                plug_closing(s->plug, winsock_error_string(err), err, 0);
+                plug_closing(s->plug, winsock_error_string(err), err);
             } else {
                 if (ret)
                     plug_receive(s->plug, 0, buf, ret);
                 else
-                    plug_closing(s->plug, NULL, 0, 0);
+                    plug_closing(s->plug, NULL, 0);
             }
         } while (ret > 0);
         return;