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
@@ -572,17 +572,22 @@
     // month", so we need to expand the month set if the constraint is present.
     $by_monthday = $this->getByMonthDay();
 
+    // Likewise, we need to generate all months if we have BYYEARDAY.
+    $by_yearday = $this->getByYearDay();
+
     while (!$this->setMonths) {
       $this->nextYear();
 
-      if ($is_monthly || $by_month || $by_monthday) {
+      $is_dynamic = $is_monthly
+        || $by_month
+        || $by_monthday
+        || $by_yearday
+        || ($scale < self::SCALE_MONTHLY);
+
+      if ($is_dynamic) {
         $months = $this->newMonthsSet(
           ($is_monthly ? $interval : 1),
           $by_month);
-      } else if ($scale < self::SCALE_MONTHLY) {
-        $months = $this->newMonthsSet(
-          1,
-          array());
       } else {
         $months = array(
           $this->cursorMonth,
@@ -768,8 +773,8 @@
       }
 
       if ($by_yearday) {
-        if (empty($by_monthday[$info['yearday']]) &&
-            empty($by_monthday[$info['-yearday']])) {
+        if (empty($by_yearday[$info['yearday']]) &&
+            empty($by_yearday[$info['-yearday']])) {
           continue;
         }
       }
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
@@ -187,6 +187,38 @@
       '19980108',
     );
 
+    $tests[] = array(
+      'BYMONTHDAY' => array(1, 3),
+      'BYDAY' => array('TU', 'TH'),
+    );
+    $expect[] = array(
+      '19980101',
+      '19980203',
+      '19980303',
+    );
+
+    $tests[] = array(
+      'BYMONTHDAY' => array(1, 3),
+      'BYDAY' => array('TU', 'TH'),
+      'BYMONTH' => array(1, 3),
+    );
+    $expect[] = array(
+      '19980101',
+      '19980303',
+      '20010301',
+    );
+
+    $tests[] = array(
+      'BYYEARDAY' => array(1, 100, 200, 365),
+      'COUNT' => 4,
+    );
+    $expect[] = array(
+      '19971231',
+      '19980101',
+      '19980410',
+      '19980719',
+    );
+
     $this->assertRules(
       array(
         'FREQ' => 'YEARLY',
@@ -228,6 +260,11 @@
         $rrule->setByMonthDay($by_monthday);
       }
 
+      $by_yearday = idx($options, 'BYYEARDAY');
+      if ($by_yearday) {
+        $rrule->setByYearDay($by_yearday);
+      }
+
       $set = id(new PhutilCalendarRecurrenceSet())
         ->addSource($rrule);