diff --git a/src/parser/calendar/data/PhutilCalendarRecurrenceRule.php b/src/parser/calendar/data/PhutilCalendarRecurrenceRule.php
--- a/src/parser/calendar/data/PhutilCalendarRecurrenceRule.php
+++ b/src/parser/calendar/data/PhutilCalendarRecurrenceRule.php
@@ -561,10 +561,15 @@
     $by_month = $this->getByMonth();
     $by_setpos = $this->getBySetPosition();
 
+    // If we have a BYMONTHDAY, we consider that set of days in every month.
+    // For example, "FREQ=YEARLY;BYMONTHDAY=3" means "the third day of every
+    // month", so we need to expand the month set if the constraint is present.
+    $by_monthday = $this->getByMonthDay();
+
     while (!$this->setMonths) {
       $this->nextYear();
 
-      if ($is_monthly || $by_month) {
+      if ($is_monthly || $by_month || $by_monthday) {
         $months = $this->newMonthsSet(
           ($is_monthly ? $interval : 1),
           $by_month);
diff --git a/src/parser/calendar/data/__tests__/PhutilCalendarRecurrenceRuleTestCase.php b/src/parser/calendar/data/__tests__/PhutilCalendarRecurrenceRuleTestCase.php
--- a/src/parser/calendar/data/__tests__/PhutilCalendarRecurrenceRuleTestCase.php
+++ b/src/parser/calendar/data/__tests__/PhutilCalendarRecurrenceRuleTestCase.php
@@ -131,6 +131,24 @@
       '20080229',
     );
 
+    $tests[] = array(
+      'BYMONTH' => array(1, 3),
+    );
+    $expect[] = array(
+      '19980102',
+      '19980302',
+      '19990102',
+    );
+
+    $tests[] = array(
+      'BYMONTHDAY' => array(1, 3),
+    );
+    $expect[] = array(
+      '19970903',
+      '19971001',
+      '19971003',
+    );
+
     $this->assertRules(
       array(
         'FREQ' => 'YEARLY',
@@ -157,6 +175,16 @@
         $rrule->setInterval($interval);
       }
 
+      $by_month = idx($options, 'BYMONTH');
+      if ($by_month) {
+        $rrule->setByMonth($by_month);
+      }
+
+      $by_monthday = idx($options, 'BYMONTHDAY');
+      if ($by_monthday) {
+        $rrule->setByMonthDay($by_monthday);
+      }
+
       $set = id(new PhutilCalendarRecurrenceSet())
         ->addSource($rrule);