diff --git a/src/main/java/org/apache/log4j/pattern/DatePatternConverter.java b/src/main/java/org/apache/log4j/pattern/DatePatternConverter.java
index c961658..901d2b8 100644
--- a/src/main/java/org/apache/log4j/pattern/DatePatternConverter.java
+++ b/src/main/java/org/apache/log4j/pattern/DatePatternConverter.java
@@ -70,7 +70,7 @@
      * This class wraps a DateFormat and forces the time zone to the
      *   default time zone before each format and parse request.
      */
-  private class DefaultZoneDateFormat extends DateFormat {
+  private static class DefaultZoneDateFormat extends DateFormat {
         /**
          * Wrapped instance of DateFormat.
          */