diff --git a/_locales/en/messages.json b/_locales/en/messages.json
index 817bfe66..c6aacb70 100644
--- a/_locales/en/messages.json
+++ b/_locales/en/messages.json
@@ -1881,6 +1881,10 @@
     "message": "If checked there is no need to select some text. The full message body will be used to get the calendar event.",
     "description": ""
   },
+  "prefs_OptionText_calendar_no_selection_missing_placeholder": {
+    "message": "The prompt must contain the placeholder {%mail_text_body_or_selected%} or {%mail_html_body_or_selected%} to enable this option. Please add one of these placeholders to the prompt or reset it to the default.",
+    "description": ""
+  },
   "customPrompts_btnCopy": {
     "message": "Copy",
     "description": ""
diff --git a/pages/get-calendar-event/mzta-get-calendar-event.js b/pages/get-calendar-event/mzta-get-calendar-event.js
index 7dc9a0e9..ca3c8ef7 100644
--- a/pages/get-calendar-event/mzta-get-calendar-event.js
+++ b/pages/get-calendar-event/mzta-get-calendar-event.js
@@ -98,6 +98,15 @@ document.addEventListener('DOMContentLoaded', async () => {
     });
 
     get_calendar_event_no_selection.addEventListener('change', async (event) => {
+        if (event.target.checked) {
+            const currentPromptText = get_calendar_event_textarea.value;
+            const hasBodyOrSelected = currentPromptText.includes('{%mail_text_body_or_selected%}') || currentPromptText.includes('{%mail_html_body_or_selected%}');
+            if (!hasBodyOrSelected) {
+                alert(browser.i18n.getMessage('prefs_OptionText_calendar_no_selection_missing_placeholder'));
+                event.target.checked = false;
+                return;
+            }
+        }
         specialPrompts.find(prompt => prompt.id === 'prompt_get_calendar_event').need_selected = event.target.checked ? '0' : '1';
         await setSpecialPrompts(specialPrompts);
         browser.runtime.sendMessage({command: "reload_menus"});