diff --git a/js/ct-events.js b/js/ct-events.js
index e013b44..7f60d1e 100644
--- a/js/ct-events.js
+++ b/js/ct-events.js
@@ -89,7 +89,7 @@ function display_event_date(item) {
 			return m("span.timerange", display_date_utc(start, utc_start_date), " - ", display_date_utc(end_day, utc_end_day_date));
 		}
 	}
-	
+
 	if (start_date === end_date) {
 		return m("span.timerange", display_datetime(start, `${start_date}, ${start_time}`), " - ", display_datetime(end, end_time));
 	} else {
@@ -102,31 +102,43 @@ function display_event_date(item) {
 	}
 }
 
-function escapeICSField(text) {
-	return text.replace(/\\/g, "\\\\")
-		.replace(/[,;]/g, "\\$&")
-		.replace(/\n/g, "\\n");
+function format_ICS_text(text) {
+	return text.replace(/[\\,;]/g, "\\$&") // escape backslash and separators
+		.replace(/\n/g, "\\n") // escape newline
+		.replace(/[\x00-\x1f]+/g, " ") // replace control characters with whitespace
+	;
+}
+
+function format_ICS_date(date) {
+	if (date) {
+		date = new Date(date);
+	} else {
+		date = new Date(); // default to "now"
+	}
+	// remove "-" and ":" separators (but keep "T"), and drop microseconds
+	return date.toISOString().replace(/-|:|\.\d+/g, "");
 }
 
 function createICSLink(item, settings) {
-	const start = new Date(item.calculated.startDate).toISOString().replace(/-|:|\.\d+/g, '');
-	const end = new Date(item.calculated.endDate).toISOString().replace(/-|:|\.\d+/g, '');
+	const start = format_ICS_date(item.calculated.startDate);
+	const end = format_ICS_date(item.calculated.endDate);
 
 	const summary = item.base.caption;
 	const description = item.base.information || "";
 	const location = item.base.address?.meetingAt || "";
 
 	// Escape special characters for ICS fields
-	const escapedSummary = escapeICSField(summary /* .replace(/['"]/g, "") */);
-	const escapedDescription = escapeICSField(description /* .replace(/['"]/g, "") */);
-	const escapedLocation = escapeICSField(location);
-	
+	const escapedSummary = format_ICS_text(summary /* .replace(/['"]/g, "") */);
+	const escapedDescription = format_ICS_text(description /* .replace(/['"]/g, "") */);
+	const escapedLocation = format_ICS_text(location);
+
 	const icsContent = `BEGIN:VCALENDAR
 VERSION:2.0
-PRODID:-//Evang Kirchengemeinde Malmsheim//Gottesdienste//EN
+PRODID:-//churchtools-next-events//EN
 BEGIN:VEVENT
-UID:${crypto.randomUUID()}@malmsheim-evangelisch.de
-DTSTAMP:${new Date().toISOString().replace(/-|:|\.\d+/g, '')}
+UID:appointment-${item.base.id}@${window.location.hostname}
+CREATED:${format_ICS_date(item.base.meta?.createdDate)}
+LAST-MODIFIED:${format_ICS_date(item.base.meta?.modifiedDate)}
 DTSTART:${start}
 DTEND:${end}
 SUMMARY:${escapedSummary}
@@ -273,7 +285,7 @@ var AppointmentLocation = {
 		if (!location) {
 			return m("[");
 		}
-		
+
 		return m("p", [
 			fa_solid_icon(settings, "location-dot"),
 			" ",
@@ -293,7 +305,7 @@ var AppointmentLink = {
 		if (!url.startsWith("http")) {
 			url = "https://" + url;
 		}
-		
+
 		return m("p", [
 			fa_solid_icon(settings, "link"),
 			" ",
@@ -389,24 +401,30 @@ async function load_events(dom_node, defaults) {
 		credentials: "omit",
 		mode: "cors",
 	}
-	
+
 	const r_cal_regex = new RegExp(settings.calendar_regex, "i");
 	const r_event_regex = new RegExp(settings.event_regex, "i");
 	const all_calendars = (await (await fetch(settings.instance + "/api/calendars", req_config)).json()).data;
 	const calendars = all_calendars.filter((calendar) => r_cal_regex.exec(calendar.name));
 	const calendar_ids = calendars.map((calendar) => calendar.id);
 
-	const filters = calendar_ids.map((cal_id) => `calendar_ids[]=${cal_id}`);
-	const from = new Date();
-	filters.push(`from=${format_date(from)}`);
-	const to = new Date(from.valueOf() + settings.days * 86400 * 1000);
-	filters.push(`to=${format_date(to)}`);
-	const query = filters.join("&");
-	const all_appointments = (await (await fetch(settings.instance + `/api/calendars/appointments?${query}`, req_config)).json()).data;
-	const appointments = all_appointments.filter((appointment) => r_event_regex.exec(appointment.base.title));
-	
-	if (appointments.length > settings.limit) {
-		appointments.length = settings.limit;
+	let appointments;
+
+	if (calendar_ids.length) {
+		const filters = calendar_ids.map((cal_id) => `calendar_ids[]=${cal_id}`);
+		const from = new Date();
+		filters.push(`from=${format_date(from)}`);
+		const to = new Date(from.valueOf() + settings.days * 86400 * 1000);
+		filters.push(`to=${format_date(to)}`);
+		const query = filters.join("&");
+		const all_appointments = (await (await fetch(settings.instance + `/api/calendars/appointments?${query}`, req_config)).json()).data;
+		appointments = all_appointments.filter((appointment) => r_event_regex.exec(appointment.base.title));
+
+		if (appointments.length > settings.limit) {
+			appointments.length = settings.limit;
+		}
+	} else {
+		appointments = [];
 	}
 
 	const Appointments = {