Index: src/main/java/org/apache/logging/log4j/core/appender/rolling/PatternProcessor.java
===================================================================
--- src/main/java/org/apache/logging/log4j/core/appender/rolling/PatternProcessor.java	(revision 1524213)
+++ src/main/java/org/apache/logging/log4j/core/appender/rolling/PatternProcessor.java	(working copy)
@@ -103,6 +103,7 @@
             return nextTime;
         }
         if (frequency == RolloverFrequency.MONTHLY) {
+        	cal.set(Calendar.MONTH, currentCal.get(Calendar.MONTH));
             increment(cal, Calendar.MONTH, increment, modulus);
             nextTime = cal.getTimeInMillis();
             cal.add(Calendar.MONTH, -1);
@@ -110,6 +111,7 @@
             return nextTime;
         }
         if (frequency == RolloverFrequency.WEEKLY) {
+        	cal.set(Calendar.WEEK_OF_YEAR, currentCal.get(Calendar.WEEK_OF_YEAR));
             increment(cal, Calendar.WEEK_OF_YEAR, increment, modulus);
             nextTime = cal.getTimeInMillis();
             cal.add(Calendar.WEEK_OF_YEAR, -1);