diff --git a/logback-core/src/main/java/ch/qos/logback/core/rolling/helper/PeriodicityType.java b/logback-core/src/main/java/ch/qos/logback/core/rolling/helper/PeriodicityType.java
index bc900f964f..4d8ee26dae 100644
--- a/logback-core/src/main/java/ch/qos/logback/core/rolling/helper/PeriodicityType.java
+++ b/logback-core/src/main/java/ch/qos/logback/core/rolling/helper/PeriodicityType.java
@@ -21,6 +21,7 @@ public enum PeriodicityType {
     // The followed list consists of valid periodicity types in increasing period lengths
     static PeriodicityType[] VALID_ORDERED_LIST = new PeriodicityType[] { TOP_OF_MILLISECOND,
             PeriodicityType.TOP_OF_SECOND, PeriodicityType.TOP_OF_MINUTE, PeriodicityType.TOP_OF_HOUR,
-            PeriodicityType.TOP_OF_DAY, PeriodicityType.TOP_OF_WEEK, PeriodicityType.TOP_OF_MONTH };
+            PeriodicityType.HALF_DAY, PeriodicityType.TOP_OF_DAY, PeriodicityType.TOP_OF_WEEK,
+            PeriodicityType.TOP_OF_MONTH };
 
 }
diff --git a/logback-core/src/main/java/ch/qos/logback/core/rolling/helper/RollingCalendar.java b/logback-core/src/main/java/ch/qos/logback/core/rolling/helper/RollingCalendar.java
index a0dcb2c677..4618542d59 100644
--- a/logback-core/src/main/java/ch/qos/logback/core/rolling/helper/RollingCalendar.java
+++ b/logback-core/src/main/java/ch/qos/logback/core/rolling/helper/RollingCalendar.java
@@ -105,6 +105,10 @@ public boolean isCollisionFree() {
             // isolated hh or KK
             return !collision(12 * MILLIS_IN_ONE_HOUR);
 
+        case HALF_DAY:
+            // isolated 'a' (AM/PM) without a date component repeats every day
+            return !collision(MILLIS_IN_ONE_DAY);
+
         case TOP_OF_DAY:
             // EE or uu
             if (collision(7 * MILLIS_IN_ONE_DAY))
@@ -198,6 +202,8 @@ public long periodBarriersCrossed(long start, long end) {
             return diff / MILLIS_IN_ONE_MINUTE;
         case TOP_OF_HOUR:
             return diff / MILLIS_IN_ONE_HOUR;
+        case HALF_DAY:
+            return diff / (12 * MILLIS_IN_ONE_HOUR);
         case TOP_OF_DAY:
             return diff / MILLIS_IN_ONE_DAY;
         case TOP_OF_WEEK:
@@ -251,6 +257,15 @@ static private Instant innerGetEndOfNextNthPeriod(Calendar cal, PeriodicityType
             cal.add(Calendar.HOUR_OF_DAY, numPeriods);
             break;
 
+        case HALF_DAY:
+            // floor to the start of the current half-day (00:00 or 12:00), then advance
+            cal.set(Calendar.HOUR_OF_DAY, cal.get(Calendar.HOUR_OF_DAY) < 12 ? 0 : 12);
+            cal.set(Calendar.MINUTE, 0);
+            cal.set(Calendar.SECOND, 0);
+            cal.set(Calendar.MILLISECOND, 0);
+            cal.add(Calendar.HOUR_OF_DAY, numPeriods * 12);
+            break;
+
         case TOP_OF_DAY:
             cal.set(Calendar.HOUR_OF_DAY, 0);
             cal.set(Calendar.MINUTE, 0);
diff --git a/logback-core/src/test/java/ch/qos/logback/core/rolling/helper/RollingCalendarTest.java b/logback-core/src/test/java/ch/qos/logback/core/rolling/helper/RollingCalendarTest.java
index 1ab14d036a..7eee2a6ba9 100644
--- a/logback-core/src/test/java/ch/qos/logback/core/rolling/helper/RollingCalendarTest.java
+++ b/logback-core/src/test/java/ch/qos/logback/core/rolling/helper/RollingCalendarTest.java
@@ -80,6 +80,17 @@ public void testPeriodicity() {
             assertEquals(PeriodicityType.TOP_OF_HOUR, rc.getPeriodicityType());
         }
 
+        {
+            // 'a' (AM/PM) without a finer time token means twice-a-day roll-over
+            RollingCalendar rc = new RollingCalendar("yyyy-MM-dd-a");
+            assertEquals(PeriodicityType.HALF_DAY, rc.getPeriodicityType());
+        }
+
+        {
+            RollingCalendar rc = new RollingCalendar("yyyy-MM-dd a");
+            assertEquals(PeriodicityType.HALF_DAY, rc.getPeriodicityType());
+        }
+
         {
             RollingCalendar rc = new RollingCalendar("yyyy-MM-dd");
             assertEquals(PeriodicityType.TOP_OF_DAY, rc.getPeriodicityType());
@@ -132,6 +143,23 @@ public void testVaryingNumberOfDailyPeriods() {
         }
     }
 
+    @Test
+    public void testVaryingNumberOfHalfDailyPeriods() {
+        RollingCalendar rc = new RollingCalendar("yyyy-MM-dd-a");
+        final long MILLIS_IN_HALF_DAY = 12 * 3600 * 1000;
+
+        for (int p = 20; p > -100; p--) {
+            long now = 1223325293589L; // Mon Oct 06 22:34:53 CEST 2008
+            Instant nowInstant = Instant.ofEpochMilli(now);
+            Instant result = rc.getEndOfNextNthPeriod(nowInstant, p);
+            long offset = rc.getTimeZone().getRawOffset() + rc.getTimeZone().getDSTSavings();
+
+            long origin = now - ((now + offset) % (MILLIS_IN_HALF_DAY));
+            long expected = origin + p * MILLIS_IN_HALF_DAY;
+            assertEquals(expected, result.toEpochMilli(), "p=" + p);
+        }
+    }
+
     // Wed Mar 23 23:07:05 CET 2016
     final long WED_2016_03_23_T_230705_CET = 1458770825333L;
 
@@ -143,6 +171,8 @@ public void testBarrierCrossingComputation() {
                 WED_2016_03_23_T_230705_CET + 3 * CoreConstants.MILLIS_IN_ONE_MINUTE, 3);
         checkPeriodBarriersCrossed("yyyy-MM-dd'T'HH", WED_2016_03_23_T_230705_CET,
                 WED_2016_03_23_T_230705_CET + 3 * CoreConstants.MILLIS_IN_ONE_HOUR, 3);
+        checkPeriodBarriersCrossed("yyyy-MM-dd-a", WED_2016_03_23_T_230705_CET,
+                WED_2016_03_23_T_230705_CET + 3 * 12 * CoreConstants.MILLIS_IN_ONE_HOUR, 3);
         checkPeriodBarriersCrossed("yyyy-MM-dd", WED_2016_03_23_T_230705_CET,
                 WED_2016_03_23_T_230705_CET + 3 * CoreConstants.MILLIS_IN_ONE_DAY, 3);
     }
@@ -164,6 +194,10 @@ public void testCollisionFreenes() {
         checkCollisionFreeness("yyyy-MM-dd KK", false);
         checkCollisionFreeness("yyyy-MM-dd KK a", true);
 
+        // half-daily
+        checkCollisionFreeness("yyyy-MM-dd-a", true);
+        checkCollisionFreeness("a", false);
+
         // daily
         checkCollisionFreeness("yyyy-MM-dd", true);
         checkCollisionFreeness("yyyy-dd", false);