diff --git a/unix/dialog.c b/unix/dialog.c
index f6c5ab54..1d9944c5 100644
--- a/unix/dialog.c
+++ b/unix/dialog.c
@@ -4224,6 +4224,7 @@ struct ca_config_box {
     GtkWidget *window;
     struct controlbox *cb;
     struct Shortcuts scs;
+    bool quit_main;
     dlgparam dp;
 };
 static struct ca_config_box *cacfg;    /* one of these, cross-instance */
@@ -4234,8 +4235,10 @@ static void cacfg_destroy(GtkWidget *widget, gpointer data)
     dlg_cleanup(&cacfg->dp);
     ctrl_free_box(cacfg->cb);
     cacfg->cb = NULL;
+    if (cacfg->quit_main)
+        gtk_main_quit();
 }
-void show_ca_config_box(dlgparam *dp)
+static void make_ca_config_box(GtkWidget *spawning_window)
 {
     if (!cacfg) {
         cacfg = snew(struct ca_config_box);
@@ -4288,8 +4291,8 @@ void show_ca_config_box(dlgparam *dp)
 
     dlg_refresh(NULL, &cacfg->dp);
 
-    if (dp) {
-        set_transient_window_pos(dp->window, cacfg->window);
+    if (spawning_window) {
+        set_transient_window_pos(spawning_window, cacfg->window);
     } else {
         gtk_window_set_position(GTK_WINDOW(cacfg->window), GTK_WIN_POS_CENTER);
     }
@@ -4300,3 +4303,15 @@ void show_ca_config_box(dlgparam *dp)
     g_signal_connect(G_OBJECT(cacfg->window), "key_press_event",
                      G_CALLBACK(win_key_press), &cacfg->dp);
 }
+
+void show_ca_config_box(dlgparam *dp)
+{
+    make_ca_config_box(dp ? dp->window : NULL);
+}
+
+void show_ca_config_box_synchronously(void)
+{
+    make_ca_config_box(NULL);
+    cacfg->quit_main = true;
+    gtk_main();
+}
diff --git a/unix/main-gtk-simple.c b/unix/main-gtk-simple.c
index e52a18d0..b08a0acc 100644
--- a/unix/main-gtk-simple.c
+++ b/unix/main-gtk-simple.c
@@ -532,6 +532,11 @@ bool do_cmdline(int argc, char **argv, bool do_everything, Conf *conf)
             pgp_fingerprints();
             exit(1);
 
+        } else if (!strcmp(p, "-host-ca") || !strcmp(p, "--host-ca") ||
+                   !strcmp(p, "-host_ca") || !strcmp(p, "--host_ca")) {
+            show_ca_config_box_synchronously();
+            exit(0);
+
         } else if (p[0] != '-') {
             /* Non-option arguments not handled by cmdline.c are errors. */
             if (do_everything) {
diff --git a/unix/platform.h b/unix/platform.h
index 7cdf4d11..6a8c7ba3 100644
--- a/unix/platform.h
+++ b/unix/platform.h
@@ -245,6 +245,7 @@ GtkWidget *create_message_box(
     bool selectable, const struct message_box_buttons *buttons,
     post_dialog_fn_t after, void *afterctx);
 #endif
+void show_ca_config_box_synchronously(void);
 
 /* window.c needs this special function in utils */
 int keysym_to_unicode(int keysym);
diff --git a/windows/putty.c b/windows/putty.c
index 83594d61..fca1d4bb 100644
--- a/windows/putty.c
+++ b/windows/putty.c
@@ -87,6 +87,10 @@ void gui_term_process_cmdline(Conf *conf, char *cmdline)
             } else if (!strcmp(p, "-pgpfp")) {
                 pgp_fingerprints_msgbox(NULL);
                 exit(1);
+            } else if (!strcmp(p, "-host-ca") || !strcmp(p, "--host-ca") ||
+                       !strcmp(p, "-host_ca") || !strcmp(p, "--host_ca")) {
+                show_ca_config_box(NULL);
+                exit(0);
             } else if (!strcmp(p, "-demo-config-box")) {
                 if (i+1 >= argc) {
                     cmdline_error("%s expects an output filename", p);