diff --git a/mac/README.mac b/mac/README.mac
index 9494c9f2..abe3a193 100644
--- a/mac/README.mac
+++ b/mac/README.mac
@@ -3,6 +3,10 @@ $Id$
 Information about PuTTY for the Mac OS
 -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
 
+This is a port of PuTTY to the Classic Mac OS.  It is a work in
+progress and should be considered unfinished and insecure.  Unless you
+know what you're doing, don't use it.
+
 Compiling it:
 
  See ../README for generic information.
@@ -83,7 +87,6 @@ Unimplemented features (should be done before release):
  * Private key files.
  * Pageant and PuTTYgen.
  * Do something with Open Application Apple Events.
- * Warn-on-close.
  * Close-on-exit.
  * Warn-on-quit.
  * Non-block cursors.
diff --git a/mac/macterm.c b/mac/macterm.c
index 78efa65f..22360e14 100644
--- a/mac/macterm.c
+++ b/mac/macterm.c
@@ -1012,9 +1012,19 @@ static pascal void mac_growtermdraghook(void)
 
 void mac_closeterm(WindowPtr window)
 {
+    int alertret;
     Session *s = mac_windowsession(window);
 
-    /* XXX warn on close */
+    if (s->cfg.warn_on_close) {
+	ParamText("\pAre you sure you want to close this session?",
+		  NULL, NULL, NULL);
+	alertret=CautionAlert(wQuestion, NULL);
+	if (alertret == 2) {
+	    /* Cancel */
+	    return;
+	}
+    }
+
     HideWindow(s->window);
     *s->prev = s->next;
     s->next->prev = s->prev;