diff --git a/network.h b/network.h
index 068e6cc6..851e1738 100644
--- a/network.h
+++ b/network.h
@@ -224,6 +224,10 @@ static inline void plug_log(
 { p->vt->log(p, type, addr, port, msg, code); }
 static inline void plug_closing(Plug *p, const char *msg, int code)
 { p->vt->closing(p, msg, code); }
+static inline void plug_closing_normal(Plug *p)
+{ p->vt->closing(p, NULL, 0); }
+static inline void plug_closing_error(Plug *p, const char *msg)
+{ p->vt->closing(p, msg, 0); }
 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)
diff --git a/proxy/cproxy.c b/proxy/cproxy.c
index d187ffec..e58c344b 100644
--- a/proxy/cproxy.c
+++ b/proxy/cproxy.c
@@ -65,15 +65,13 @@ int proxy_socks5_handlechap (ProxySocket *p)
              * number of attributes
              */
             if (data[0] != 0x01) {
-                plug_closing(p->plug, "Proxy error: SOCKS proxy wants"
-                             " a different CHAP version",
-                             PROXY_ERROR_GENERAL);
+                plug_closing_error(p->plug, "Proxy error: SOCKS proxy wants "
+                                   "a different CHAP version");
                 return 1;
             }
             if (data[1] == 0x00) {
-                plug_closing(p->plug, "Proxy error: SOCKS proxy won't"
-                             " negotiate CHAP with us",
-                             PROXY_ERROR_GENERAL);
+                plug_closing_error(p->plug, "Proxy error: SOCKS proxy won't "
+                                   "negotiate CHAP with us");
                 return 1;
             }
             p->chap_num_attributes = data[1];
@@ -103,9 +101,8 @@ int proxy_socks5_handlechap (ProxySocket *p)
                 if (data[0] == 0x00)
                     p->state = 2;
                 else {
-                    plug_closing(p->plug, "Proxy error: SOCKS proxy"
-                                 " refused CHAP authentication",
-                                 PROXY_ERROR_GENERAL);
+                    plug_closing_error(p->plug, "Proxy error: SOCKS proxy "
+                                       "refused CHAP authentication");
                     return 1;
                 }
               break;
@@ -122,10 +119,9 @@ int proxy_socks5_handlechap (ProxySocket *p)
               case 0x11:
                 /* Chose a protocol */
                 if (data[0] != 0x85) {
-                    plug_closing(p->plug, "Proxy error: Server chose "
-                                 "CHAP of other than HMAC-MD5 but we "
-                                 "didn't offer it!",
-                                 PROXY_ERROR_GENERAL);
+                    plug_closing_error(p->plug, "Proxy error: Server chose "
+                                       "CHAP of other than HMAC-MD5 but we "
+                                       "didn't offer it!");
                     return 1;
                 }
               break;
@@ -172,8 +168,7 @@ int proxy_socks5_selectchap(ProxySocket *p)
 
         p->state = 8;
     } else
-        plug_closing(p->plug, "Proxy error: Server chose "
-                     "CHAP authentication but we didn't offer it!",
-                     PROXY_ERROR_GENERAL);
+        plug_closing_error(p->plug, "Proxy error: Server chose "
+                           "CHAP authentication but we didn't offer it!");
     return 1;
 }
diff --git a/proxy/nocproxy.c b/proxy/nocproxy.c
index cdc28a39..ed9c3ffd 100644
--- a/proxy/nocproxy.c
+++ b/proxy/nocproxy.c
@@ -17,19 +17,16 @@ void proxy_socks5_offerencryptedauth(BinarySink *bs)
     /* For telnet, don't add any new encrypted authentication routines */
 }
 
-int proxy_socks5_handlechap (ProxySocket *p)
+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);
+    plug_closing_error(p->plug, "Proxy error: Trying to handle a "
+                       "SOCKS5 CHAP request in telnet-only build");
     return 1;
 }
 
 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);
+    plug_closing_error(p->plug, "Proxy error: Trying to handle a "
+                       "SOCKS5 CHAP request in telnet-only build");
     return 1;
 }
diff --git a/proxy/proxy.c b/proxy/proxy.c
index 69b32866..d4963db4 100644
--- a/proxy/proxy.c
+++ b/proxy/proxy.c
@@ -671,8 +671,8 @@ int proxy_http_negotiate (ProxySocket *p, int change)
             /* We can't rely on whether the %n incremented the sscanf return */
             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);
+                plug_closing_error(p->plug, "Proxy error: "
+                                   "HTTP response was absent");
                 sfree(data);
                 return 1;
             }
@@ -687,7 +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);
+                plug_closing_error(p->plug, buf);
                 sfree(buf);
                 sfree(data);
                 return 1;
@@ -737,8 +737,7 @@ int proxy_http_negotiate (ProxySocket *p, int change)
         }
     }
 
-    plug_closing(p->plug, "Proxy error: unexpected proxy error",
-                 PROXY_ERROR_UNEXPECTED);
+    plug_closing_error(p->plug, "Proxy error: unexpected proxy error");
     return 1;
 }
 
@@ -854,9 +853,9 @@ int proxy_socks4_negotiate (ProxySocket *p, int change)
             bufchain_fetch(&p->pending_input_data, data, 8);
 
             if (data[0] != 0) {
-                plug_closing(p->plug, "Proxy error: SOCKS proxy responded with "
-                                      "unexpected reply code version",
-                             PROXY_ERROR_GENERAL);
+                plug_closing_error(p->plug, "Proxy error: SOCKS proxy "
+                                   "responded with unexpected "
+                                   "reply code version");
                 return 1;
             }
 
@@ -864,17 +863,17 @@ 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);
+                    plug_closing_error(p->plug, "Proxy error: SOCKS server "
+                                       "wanted IDENTD on client");
                     break;
                   case 93:
-                    plug_closing(p->plug, "Proxy error: Username and IDENTD on client don't agree",
-                                 PROXY_ERROR_GENERAL);
+                    plug_closing_error(p->plug, "Proxy error: Username and "
+                                       "IDENTD on client don't agree");
                     break;
                   case 91:
                   default:
-                    plug_closing(p->plug, "Proxy error: Error while communicating with proxy",
-                                 PROXY_ERROR_GENERAL);
+                    plug_closing_error(p->plug, "Proxy error: Error while "
+                                       "communicating with proxy");
                     break;
                 }
 
@@ -890,8 +889,7 @@ int proxy_socks4_negotiate (ProxySocket *p, int change)
         }
     }
 
-    plug_closing(p->plug, "Proxy error: unexpected proxy error",
-                 PROXY_ERROR_UNEXPECTED);
+    plug_closing_error(p->plug, "Proxy error: unexpected proxy error");
     return 1;
 }
 
@@ -996,8 +994,8 @@ int proxy_socks5_negotiate (ProxySocket *p, int change)
             bufchain_fetch(&p->pending_input_data, data, 2);
 
             if (data[0] != 5) {
-                plug_closing(p->plug, "Proxy error: SOCKS proxy returned unexpected version",
-                             PROXY_ERROR_GENERAL);
+                plug_closing_error(p->plug, "Proxy error: SOCKS proxy "
+                                   "returned unexpected version");
                 return 1;
             }
 
@@ -1006,8 +1004,8 @@ int proxy_socks5_negotiate (ProxySocket *p, int change)
             else if (data[1] == 0x02) p->state = 5; /* username/password authentication */
             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);
+                plug_closing_error(p->plug, "Proxy error: SOCKS proxy did not "
+                                   "accept our authentication");
                 return 1;
             }
             bufchain_consume(&p->pending_input_data, 2);
@@ -1030,17 +1028,15 @@ int proxy_socks5_negotiate (ProxySocket *p, int change)
             bufchain_fetch(&p->pending_input_data, data, 2);
 
             if (data[0] != 1) {
-                plug_closing(p->plug, "Proxy error: SOCKS password "
-                             "subnegotiation contained wrong version number",
-                             PROXY_ERROR_GENERAL);
+                plug_closing_error(p->plug, "Proxy error: SOCKS password "
+                                   "subnegotiation contained wrong version "
+                                   "number");
                 return 1;
             }
 
             if (data[1] != 0) {
-
-                plug_closing(p->plug, "Proxy error: SOCKS proxy refused"
-                             " password authentication",
-                             PROXY_ERROR_GENERAL);
+                plug_closing_error(p->plug, "Proxy error: SOCKS proxy refused "
+                                   "password authentication");
                 return 1;
             }
 
@@ -1142,8 +1138,8 @@ int proxy_socks5_negotiate (ProxySocket *p, int change)
             bufchain_fetch(&p->pending_input_data, data, 5);
 
             if (data[0] != 5) {
-                plug_closing(p->plug, "Proxy error: SOCKS proxy returned wrong version number",
-                             PROXY_ERROR_GENERAL);
+                plug_closing_error(p->plug, "Proxy error: SOCKS proxy "
+                                   "returned wrong version number");
                 return 1;
             }
 
@@ -1166,7 +1162,7 @@ int proxy_socks5_negotiate (ProxySocket *p, int change)
                                    data[1]);
                     break;
                 }
-                plug_closing(p->plug, buf, PROXY_ERROR_GENERAL);
+                plug_closing_error(p->plug, buf);
 
                 return 1;
             }
@@ -1180,9 +1176,8 @@ int proxy_socks5_negotiate (ProxySocket *p, int change)
               case 4: len += 16; break;/* IPv6 address */
               case 3: len += 1+(unsigned char)data[4]; break; /* domain name */
               default:
-                plug_closing(p->plug, "Proxy error: SOCKS proxy returned "
-                             "unrecognised address format",
-                             PROXY_ERROR_GENERAL);
+                plug_closing_error(p->plug, "Proxy error: SOCKS proxy "
+                                   "returned unrecognised address format");
                 return 1;
             }
             if (bufchain_size(&p->pending_input_data) < len)
@@ -1196,8 +1191,8 @@ 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);
+            plug_closing_error(p->plug, "Proxy error: We don't support "
+                               "GSSAPI authentication");
             return 1;
         }
 
@@ -1223,10 +1218,9 @@ int proxy_socks5_negotiate (ProxySocket *p, int change)
                 strbuf_free(auth);
                 p->state = 7;
             } else
-                plug_closing(p->plug, "Proxy error: Server chose "
-                             "username/password authentication but we "
-                             "didn't offer it!",
-                             PROXY_ERROR_GENERAL);
+                plug_closing_error(p->plug, "Proxy error: Server chose "
+                                   "username/password authentication "
+                                   "but we didn't offer it!");
             return 1;
         }
 
@@ -1238,8 +1232,7 @@ int proxy_socks5_negotiate (ProxySocket *p, int change)
 
     }
 
-    plug_closing(p->plug, "Proxy error: Unexpected proxy error",
-                 PROXY_ERROR_UNEXPECTED);
+    plug_closing_error(p->plug, "Proxy error: Unexpected proxy error");
     return 1;
 }
 
@@ -1509,7 +1502,6 @@ int proxy_telnet_negotiate (ProxySocket *p, int change)
         return 1;
     }
 
-    plug_closing(p->plug, "Proxy error: Unexpected proxy error",
-                 PROXY_ERROR_UNEXPECTED);
+    plug_closing_error(p->plug, "Proxy error: Unexpected proxy error");
     return 1;
 }
diff --git a/proxy/proxy.h b/proxy/proxy.h
index 9dca87d1..3ec3261c 100644
--- a/proxy/proxy.h
+++ b/proxy/proxy.h
@@ -10,9 +10,6 @@
 #ifndef PUTTY_PROXY_H
 #define PUTTY_PROXY_H
 
-#define PROXY_ERROR_GENERAL 8000
-#define PROXY_ERROR_UNEXPECTED 8001
-
 typedef struct ProxySocket ProxySocket;
 
 struct ProxySocket {
diff --git a/proxy/sshproxy.c b/proxy/sshproxy.c
index c3785bd0..fd9afc4e 100644
--- a/proxy/sshproxy.c
+++ b/proxy/sshproxy.c
@@ -234,7 +234,7 @@ 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);
+        plug_closing_normal(sp->plug);
     }
 }
 
@@ -316,7 +316,10 @@ static void sshproxy_send_close(SshProxy *sp)
         plug_log(sp->plug, PLUGLOG_CONNECT_FAILED, sp->addr, sp->port,
                  sp->errmsg, 0);
 
-    plug_closing(sp->plug, sp->errmsg, 0);
+    if (sp->errmsg)
+        plug_closing_error(sp->plug, sp->errmsg);
+    else
+        plug_closing_normal(sp->plug);
 }
 
 static void sshproxy_notify_remote_disconnect_callback(void *vctx)
diff --git a/unix/fd-socket.c b/unix/fd-socket.c
index 48d7dc8b..013c5361 100644
--- a/unix/fd-socket.c
+++ b/unix/fd-socket.c
@@ -158,7 +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);
+    plug_closing_errno(fds->plug, fds->pending_error);
 }
 
 static int fdsocket_try_send(FdSocket *fds)
@@ -270,9 +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);
+            plug_closing_errno(fds->plug, errno);
         } else {
-            plug_closing(fds->plug, NULL, 0);
+            plug_closing_normal(fds->plug);
         }
     }
 }
diff --git a/unix/network.c b/unix/network.c
index d2d426ed..32cc3c9e 100644
--- a/unix/network.c
+++ b/unix/network.c
@@ -1084,6 +1084,11 @@ void *sk_getxdmdata(Socket *sock, int *lenp)
     return buf;
 }
 
+void plug_closing_errno(Plug *plug, int error)
+{
+    plug_closing(plug, strerror(error), error);
+}
+
 /*
  * Deal with socket errors detected in try_send().
  */
@@ -1101,7 +1106,7 @@ 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);
+    plug_closing_errno(s->plug, s->pending_error);
 }
 
 /*
@@ -1295,10 +1300,10 @@ static void net_select_result(int fd, int event)
              */
             ret = recv(s->s, buf, sizeof(buf), MSG_OOB);
             noise_ultralight(NOISE_SOURCE_IOLEN, ret);
-            if (ret <= 0) {
-                plug_closing(s->plug,
-                             ret == 0 ? "Internal networking trouble" :
-                             strerror(errno), errno);
+            if (ret == 0) {
+                plug_closing_error(s->plug, "Internal networking trouble");
+            } else if (ret < 0) {
+                plug_closing_errno(s->plug, errno);
             } else {
                 /*
                  * Receiving actual data on a socket means we can
@@ -1384,11 +1389,11 @@ static void net_select_result(int fd, int event)
             }
         }
         if (ret < 0) {
-            plug_closing(s->plug, strerror(errno), errno);
+            plug_closing_errno(s->plug, errno);
         } else if (0 == ret) {
             s->incomingeof = true;     /* stop trying to read now */
             uxsel_tell(s);
-            plug_closing(s->plug, NULL, 0);
+            plug_closing_normal(s->plug);
         } else {
             /*
              * Receiving actual data on a socket means we can
@@ -1438,7 +1443,7 @@ static void net_select_result(int fd, int event)
                         err = try_connect(s);
                     }
                     if (err) {
-                        plug_closing(s->plug, strerror(err), err);
+                        plug_closing_errno(s->plug, err);
                         return;      /* socket is now presumably defunct */
                     }
                     if (!s->connected)
diff --git a/unix/platform.h b/unix/platform.h
index b4f5a008..79b171ca 100644
--- a/unix/platform.h
+++ b/unix/platform.h
@@ -458,4 +458,7 @@ bool cliloop_no_pw_setup(void *ctx, pollwrapper *pw);
 void cliloop_no_pw_check(void *ctx, pollwrapper *pw);
 bool cliloop_always_continue(void *ctx, bool, bool);
 
+/* network.c: network error reporting helper taking an OS error code */
+void plug_closing_errno(Plug *plug, int error);
+
 #endif /* PUTTY_UNIX_PLATFORM_H */
diff --git a/windows/handle-socket.c b/windows/handle-socket.c
index 066d2373..32479d64 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);
+        plug_closing_error(hs->plug, "Read error from handle");
         return 0;
     } else if (len == 0) {
-        plug_closing(hs->plug, NULL, 0);
+        plug_closing_normal(hs->plug);
         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);
+        plug_closing_system_error(hs->plug, err);
         return;
     }
 
diff --git a/windows/network.c b/windows/network.c
index 17c80cb4..b5b5ab0e 100644
--- a/windows/network.c
+++ b/windows/network.c
@@ -1335,6 +1335,16 @@ static void sk_net_close(Socket *sock)
     sfree(s);
 }
 
+void plug_closing_system_error(Plug *plug, DWORD error)
+{
+    plug_closing(plug, win_strerror(error), error);
+}
+
+void plug_closing_winsock_error(Plug *plug, DWORD error)
+{
+    plug_closing(plug, winsock_error_string(error), error);
+}
+
 /*
  * Deal with socket errors detected in try_send().
  */
@@ -1352,8 +1362,7 @@ 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);
+    plug_closing_winsock_error(s->plug, s->pending_error);
 }
 
 /*
@@ -1528,7 +1537,7 @@ void select_result(WPARAM wParam, LPARAM lParam)
             }
         }
         if (err != 0)
-            plug_closing(s->plug, winsock_error_string(err), err);
+            plug_closing_winsock_error(s->plug, err);
         return;
     }
 
@@ -1590,9 +1599,9 @@ void select_result(WPARAM wParam, LPARAM lParam)
             }
         }
         if (ret < 0) {
-            plug_closing(s->plug, winsock_error_string(err), err);
+            plug_closing_winsock_error(s->plug, err);
         } else if (0 == ret) {
-            plug_closing(s->plug, NULL, 0);
+            plug_closing_normal(s->plug);
         } else {
             plug_receive(s->plug, atmark ? 0 : 1, buf, ret);
         }
@@ -1608,7 +1617,7 @@ 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);
+            plug_closing_winsock_error(s->plug, err);
         } else {
             plug_receive(s->plug, 2, buf, ret);
         }
@@ -1631,12 +1640,12 @@ void select_result(WPARAM wParam, LPARAM lParam)
                 err = p_WSAGetLastError();
                 if (err == WSAEWOULDBLOCK)
                     break;
-                plug_closing(s->plug, winsock_error_string(err), err);
+                plug_closing_winsock_error(s->plug, err);
             } else {
                 if (ret)
                     plug_receive(s->plug, 0, buf, ret);
                 else
-                    plug_closing(s->plug, NULL, 0);
+                    plug_closing_normal(s->plug);
             }
         } while (ret > 0);
         return;
diff --git a/windows/platform.h b/windows/platform.h
index cf76566b..0a1a6ef7 100644
--- a/windows/platform.h
+++ b/windows/platform.h
@@ -730,4 +730,8 @@ char *handle_restrict_acl_cmdline_prefix(char *cmdline);
 bool handle_special_sessionname_cmdline(char *cmdline, Conf *conf);
 bool handle_special_filemapping_cmdline(char *cmdline, Conf *conf);
 
+/* network.c: network error reporting helpers taking OS error code */
+void plug_closing_system_error(Plug *plug, DWORD error);
+void plug_closing_winsock_error(Plug *plug, DWORD error);
+
 #endif /* PUTTY_WINDOWS_PLATFORM_H */