diff --git a/raw.c b/raw.c
index 10e9ce64..e7a159cd 100644
--- a/raw.c
+++ b/raw.c
@@ -41,7 +41,7 @@ static int raw_closing(Plug plug, char *error_msg, int error_code,
     if (error_msg) {
 	/* A socket error has occurred. */
 	logevent(raw->frontend, error_msg);
-	connection_fatal("%s", error_msg);
+	connection_fatal(raw->frontend, "%s", error_msg);
     }				       /* Otherwise, the remote side closed the connection normally. */
     return 0;
 }
diff --git a/rlogin.c b/rlogin.c
index c12a0802..aa8dc0dd 100644
--- a/rlogin.c
+++ b/rlogin.c
@@ -43,7 +43,7 @@ static int rlogin_closing(Plug plug, char *error_msg, int error_code,
     if (error_msg) {
 	/* A socket error has occurred. */
 	logevent(rlogin->frontend, error_msg);
-	connection_fatal("%s", error_msg);
+	connection_fatal(rlogin->frontend, "%s", error_msg);
     }				       /* Otherwise, the remote side closed the connection normally. */
     return 0;
 }
diff --git a/ssh.c b/ssh.c
index 81ca0c87..11683c0e 100644
--- a/ssh.c
+++ b/ssh.c
@@ -2085,7 +2085,7 @@ static int ssh_closing(Plug plug, char *error_msg, int error_code,
     if (error_msg) {
 	/* A socket error has occurred. */
 	logevent(error_msg);
-	connection_fatal(ssh->frontend, error_msg);
+	connection_fatal(ssh->frontend, "%s", error_msg);
     } else {
 	/* Otherwise, the remote side closed the connection normally. */
     }
diff --git a/telnet.c b/telnet.c
index e3fff49f..d358f82f 100644
--- a/telnet.c
+++ b/telnet.c
@@ -643,7 +643,7 @@ static int telnet_closing(Plug plug, char *error_msg, int error_code,
     if (error_msg) {
 	/* A socket error has occurred. */
 	logevent(telnet->frontend, error_msg);
-	connection_fatal("%s", error_msg);
+	connection_fatal(telnet->frontend, "%s", error_msg);
     }				       /* Otherwise, the remote side closed the connection normally. */
     return 0;
 }
diff --git a/window.c b/window.c
index 32ed507f..6d306f56 100644
--- a/window.c
+++ b/window.c
@@ -930,13 +930,15 @@ void set_raw_mouse_mode(void *frontend, int activate)
 void connection_fatal(void *frontend, char *fmt, ...)
 {
     va_list ap;
-    char stuff[200], morestuff[100];
+    char *stuff, morestuff[100];
 
     va_start(ap, fmt);
-    vsprintf(stuff, fmt, ap);
+    stuff = dupvprintf(fmt, ap);
     va_end(ap);
     sprintf(morestuff, "%.70s Fatal Error", appname);
     MessageBox(hwnd, stuff, morestuff, MB_ICONERROR | MB_OK);
+    sfree(stuff);
+
     if (cfg.close_on_exit == FORCE_ON)
 	PostQuitMessage(1);
     else {
@@ -953,13 +955,14 @@ void connection_fatal(void *frontend, char *fmt, ...)
 void cmdline_error(char *fmt, ...)
 {
     va_list ap;
-    char stuff[200], morestuff[100];
+    char *stuff, morestuff[100];
 
     va_start(ap, fmt);
-    vsprintf(stuff, fmt, ap);
+    stuff = dupvprintf(fmt, ap);
     va_end(ap);
     sprintf(morestuff, "%.70s Command Line Error", appname);
     MessageBox(hwnd, stuff, morestuff, MB_ICONERROR | MB_OK);
+    sfree(stuff);
     exit(1);
 }
 
@@ -4302,13 +4305,14 @@ void optimised_move(void *frontend, int to, int from, int lines)
 void fatalbox(char *fmt, ...)
 {
     va_list ap;
-    char stuff[200], morestuff[100];
+    char *stuff, morestuff[100];
 
     va_start(ap, fmt);
-    vsprintf(stuff, fmt, ap);
+    stuff = dupvprintf(fmt, ap);
     va_end(ap);
     sprintf(morestuff, "%.70s Fatal Error", appname);
     MessageBox(hwnd, stuff, morestuff, MB_ICONERROR | MB_OK);
+    sfree(stuff);
     cleanup_exit(1);
 }
 
@@ -4318,14 +4322,15 @@ void fatalbox(char *fmt, ...)
 void modalfatalbox(char *fmt, ...)
 {
     va_list ap;
-    char stuff[200], morestuff[100];
+    char *stuff, morestuff[100];
 
     va_start(ap, fmt);
-    vsprintf(stuff, fmt, ap);
+    stuff = dupvprintf(fmt, ap);
     va_end(ap);
     sprintf(morestuff, "%.70s Fatal Error", appname);
     MessageBox(hwnd, stuff, morestuff,
 	       MB_SYSTEMMODAL | MB_ICONERROR | MB_OK);
+    sfree(stuff);
     cleanup_exit(1);
 }