Refactor "GMT" magic string.
diff --git a/src/main/java/org/apache/commons/lang3/time/FastDateParser.java b/src/main/java/org/apache/commons/lang3/time/FastDateParser.java
index 27eca47..94a5d97 100644
--- a/src/main/java/org/apache/commons/lang3/time/FastDateParser.java
+++ b/src/main/java/org/apache/commons/lang3/time/FastDateParser.java
@@ -921,7 +921,7 @@
             if (value.equals("Z")) {
                 cal.setTimeZone(TimeZone.getTimeZone("UTC"));
             } else {
-                cal.setTimeZone(TimeZone.getTimeZone("GMT" + value));
+                cal.setTimeZone(TimeZone.getTimeZone(TimeZones.GMT_ID + value));
             }
         }