diff --git a/plugins/calendar/calendar.php b/plugins/calendar/calendar.php
index ddaa4273..092a2247 100644
--- a/plugins/calendar/calendar.php
+++ b/plugins/calendar/calendar.php
@@ -1439,6 +1439,23 @@ class calendar extends rcube_plugin
    */
   private function _recurrence_text($rrule)
   {
+    // derive missing FREQ and INTERVAL from RDATE list
+    if (empty($rrule['FREQ']) && !empty($rrule['RDATE'])) {
+      $first = $rrule['RDATE'][0];
+      $second = $rrule['RDATE'][1];
+      if (is_a($first, 'DateTime') && is_a($second, 'DateTime')) {
+        $diff = $first->diff($second);
+        foreach (array('y' => 'YEARLY', 'm' => 'MONTHLY', 'd' => 'DAILY') as $k => $freq) {
+          if ($diff->$k != 0) {
+            $rrule['FREQ'] = $freq;
+            $rrule['INTERVAL'] = $diff->$k;
+            break;
+          }
+        }
+      }
+      $rrule['UNTIL'] = end($rrule['RDATE']);
+    }
+
     // TODO: finish this
     $freq = sprintf('%s %d ', $this->gettext('every'), $rrule['INTERVAL']);
     $details = '';
diff --git a/plugins/calendar/lib/Horde_Date_Recurrence.php b/plugins/calendar/lib/Horde_Date_Recurrence.php
index 81f0857d..35f884c7 100644
--- a/plugins/calendar/lib/Horde_Date_Recurrence.php
+++ b/plugins/calendar/lib/Horde_Date_Recurrence.php
@@ -126,6 +126,13 @@ class Horde_Date_Recurrence
      */
     public $recurMonths = array();
 
+    /**
+     * RDATE recurrence values
+     *
+     * @var array
+     */
+    public $rdates = array();
+
     /**
      * All the exceptions from recurrence for this event.
      *
@@ -427,7 +434,7 @@ class Horde_Date_Recurrence
             return clone $this->start;
         }
 
-        if ($this->recurInterval == 0) {
+        if ($this->recurInterval == 0 && empty($this->rdates)) {
             return false;
         }
 
@@ -779,6 +786,19 @@ class Horde_Date_Recurrence
             return $next;
         }
 
+        // fall-back to RDATE properties
+        if (!empty($this->rdates)) {
+            $next = clone $this->start;
+            foreach ($this->rdates as $rdate) {
+                $next->year  = $rdate->year;
+                $next->month = $rdate->month;
+                $next->mday  = $rdate->mday;
+                if ($next->compareDateTime($after) > 0) {
+                    return $next;
+                }
+            }
+        }
+
         // We didn't find anything, the recurType was bad, or something else
         // went wrong - return false.
         return false;
@@ -834,6 +854,18 @@ class Horde_Date_Recurrence
         return false;
     }
 
+    /**
+     * Adds an absolute recurrence date.
+     *
+     * @param integer $year   The year of the instance.
+     * @param integer $month  The month of the instance.
+     * @param integer $mday   The day of the month of the instance.
+     */
+    public function addRDate($year, $month, $mday)
+    {
+        $this->rdates[] = new Horde_Date($year, $month, $mday);
+    }
+
     /**
      * Adds an exception to a recurring event.
      *
diff --git a/plugins/calendar/lib/calendar_recurrence.php b/plugins/calendar/lib/calendar_recurrence.php
index d4a36412..5c218523 100644
--- a/plugins/calendar/lib/calendar_recurrence.php
+++ b/plugins/calendar/lib/calendar_recurrence.php
@@ -60,6 +60,10 @@ class calendar_recurrence
       foreach ($event['recurrence']['EXDATE'] as $exdate)
         $this->engine->addException($exdate->format('Y'), $exdate->format('n'), $exdate->format('j'));
     }
+    if (is_array($event['recurrence']['RDATE'])) {
+      foreach ($event['recurrence']['RDATE'] as $rdate)
+        $this->engine->addRDate($rdate->format('Y'), $rdate->format('n'), $rdate->format('j'));
+    }
   }
 
   /**