diff --git a/plugins/libcalendaring/libcalendaring.php b/plugins/libcalendaring/libcalendaring.php
index 47cf67e8..05465b06 100644
--- a/plugins/libcalendaring/libcalendaring.php
+++ b/plugins/libcalendaring/libcalendaring.php
@@ -313,10 +313,16 @@ class libcalendaring extends rcube_plugin
      */
     public static function parse_alaram_value($val)
     {
-        if ($val[0] == '@')
+        if ($val[0] == '@') {
             return array(substr($val, 1));
-        else if (preg_match('/([+-])P?T?(\d+)([HMSDW])/', $val, $m))
-            return array($m[2], $m[1].$m[3]);
+        }
+        else if (preg_match('/([+-])P?(T?\d+[HMSDW])+/', $val, $m) && preg_match_all('/T?(\d+)([HMSDW])/', $val, $m2, PREG_SET_ORDER)) {
+            foreach ($m2 as $seg) {
+                if ($seg[1] > 0) {  // ignore zero values
+                    return array($seg[1], $m[1].$seg[2], $m[1].$seg[1].$seg[2]);
+                }
+            }
+        }
 
         return false;
     }
diff --git a/plugins/libcalendaring/libvcalendar.php b/plugins/libcalendaring/libvcalendar.php
index 24781c93..245f8194 100644
--- a/plugins/libcalendaring/libvcalendar.php
+++ b/plugins/libcalendaring/libvcalendar.php
@@ -115,10 +115,9 @@ class libvcalendar
         try {
             // estimate the memory usage and try to avoid fatal errors when allowed memory gets exhausted
             $count = substr_count($vcal, 'BEGIN:VEVENT');
-            $memory_available = parse_bytes(ini_get('memory_limit')) - (function_exists('memory_get_usage') ? memory_get_usage() : 16*1024*1024);
             $expected_memory = $count * 70*1024;  // assume ~ 70K per event (empirically determined)
 
-            if ($memory_available > 0 && $expected_memory > $memory_available) {
+            if (!rcube_utils::mem_check($expected_memory)) {
                 throw new Exception("iCal file too big");
             }
 
@@ -448,8 +447,8 @@ class libvcalendar
                             $trigger = '@' . $prop->getDateTime()->format('U');
                         }
                     }
-                    if (!$trigger) {
-                        $trigger = preg_replace('/PT?/', '', $prop->value);
+                    if (!$trigger && ($values = libcalendaring::parse_alaram_value($prop->value))) {
+                        $trigger = $values[2];
                     }
                     break;
 
diff --git a/plugins/libcalendaring/tests/libvcalendar.php b/plugins/libcalendaring/tests/libvcalendar.php
index 34044736..4bb79411 100644
--- a/plugins/libcalendaring/tests/libvcalendar.php
+++ b/plugins/libcalendaring/tests/libvcalendar.php
@@ -139,15 +139,35 @@ class libvcalendar_test extends PHPUnit_Framework_TestCase
         $this->assertEquals(2, count($rrule['EXDATE']),          "Recurrence EXDATEs");
         $this->assertInstanceOf('DateTime', $rrule['EXDATE'][0], "Recurrence EXDATE as DateTime");
 
-        // alarms
+        // categories, class
+        $this->assertEquals('libcalendaring tests', join(',', (array)$event['categories']), "Event categories");
+        $this->assertEquals('confidential', $event['sensitivity'], "Class/sensitivity = confidential");
+    }
+
+    /**
+     * @depends test_import_from_file
+     */
+    function test_alarms()
+    {
+        $ical = new libvcalendar();
+
+        $events = $ical->import_from_file(__DIR__ . '/resources/recurring.ics', 'UTF-8');
+        $event = $events[0];
+
         $this->assertEquals('-12H:DISPLAY', $event['alarms'], "Serialized alarms string");
         $alarm = libcalendaring::parse_alaram_value($event['alarms']);
         $this->assertEquals('12', $alarm[0], "Alarm value");
         $this->assertEquals('-H', $alarm[1], "Alarm unit");
 
-        // categories, class
-        $this->assertEquals('libcalendaring tests', join(',', (array)$event['categories']), "Event categories");
-        $this->assertEquals('confidential', $event['sensitivity'], "Class/sensitivity = confidential");
+        // alarm trigger with 0 values
+        $events = $ical->import_from_file(__DIR__ . '/resources/alarms.ics', 'UTF-8');
+        $event = $events[0];
+
+        $this->assertEquals('-30M:DISPLAY', $event['alarms'], "Stripped alarm string");
+        $alarm = libcalendaring::parse_alaram_value($event['alarms']);
+        $this->assertEquals('30', $alarm[0], "Alarm value");
+        $this->assertEquals('-M', $alarm[1], "Alarm unit");
+        $this->assertEquals('-30M', $alarm[2], "Alarm string");
     }
 
     /**
diff --git a/plugins/libcalendaring/tests/resources/alarms.ics b/plugins/libcalendaring/tests/resources/alarms.ics
new file mode 100644
index 00000000..a9d7b195
--- /dev/null
+++ b/plugins/libcalendaring/tests/resources/alarms.ics
@@ -0,0 +1,43 @@
+BEGIN:VCALENDAR
+VERSION:2.0
+PRODID:-//Apple Inc.//iCal 5.0.3//EN
+CALSCALE:GREGORIAN
+BEGIN:VTIMEZONE
+TZID:Europe/Zurich
+BEGIN:DAYLIGHT
+TZOFFSETFROM:+0100
+RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=-1SU
+DTSTART:19810329T020000
+TZNAME:CEST
+TZOFFSETTO:+0200
+END:DAYLIGHT
+BEGIN:STANDARD
+TZOFFSETFROM:+0200
+RRULE:FREQ=YEARLY;BYMONTH=10;BYDAY=-1SU
+DTSTART:19961027T030000
+TZNAME:CET
+TZOFFSETTO:+0100
+END:STANDARD
+END:VTIMEZONE
+
+BEGIN:VEVENT
+UID:1dq52u617gkfqrr4uo1i2uh70
+CREATED:20130924T221822Z
+DESCRIPTION:
+DTSTART:20130818T230000Z
+DTEND:20130819T010000Z
+DTSTAMP:20130824T235608Z
+LAST-MODIFIED:20130924T222118Z
+LOCATION:
+SEQUENCE:2
+STATUS:CONFIRMED
+SUMMARY:Alarms test
+TRANSP:OPAQUE
+BEGIN:VALARM
+ACTION:DISPLAY
+DESCRIPTION:This is an event reminder
+TRIGGER:-P0DT0H30M0S
+END:VALARM
+END:VEVENT
+
+END:VCALENDAR