Index: /trunk/src/org/openstreetmap/josm/data/SystemOfMeasurement.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/data/SystemOfMeasurement.java	(revision 10214)
+++ /trunk/src/org/openstreetmap/josm/data/SystemOfMeasurement.java	(revision 10215)
@@ -5,4 +5,5 @@
 
 import java.text.NumberFormat;
+import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.Locale;
@@ -68,9 +69,10 @@
     public static final Map<String, SystemOfMeasurement> ALL_SYSTEMS;
     static {
-        ALL_SYSTEMS = new LinkedHashMap<>();
-        ALL_SYSTEMS.put(marktr("Metric"), METRIC);
-        ALL_SYSTEMS.put(marktr("Chinese"), CHINESE);
-        ALL_SYSTEMS.put(marktr("Imperial"), IMPERIAL);
-        ALL_SYSTEMS.put(marktr("Nautical Mile"), NAUTICAL_MILE);
+        Map<String, SystemOfMeasurement> map = new LinkedHashMap<>();
+        map.put(marktr("Metric"), METRIC);
+        map.put(marktr("Chinese"), CHINESE);
+        map.put(marktr("Imperial"), IMPERIAL);
+        map.put(marktr("Nautical Mile"), NAUTICAL_MILE);
+        ALL_SYSTEMS = Collections.unmodifiableMap(map);
     }
 
Index: /trunk/src/org/openstreetmap/josm/data/gpx/GpxConstants.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/data/gpx/GpxConstants.java	(revision 10214)
+++ /trunk/src/org/openstreetmap/josm/data/gpx/GpxConstants.java	(revision 10215)
@@ -4,4 +4,5 @@
 import java.util.Arrays;
 import java.util.Collection;
+import java.util.Collections;
 import java.util.List;
 
@@ -89,17 +90,17 @@
      * Ordered list of all possible waypoint keys.
      */
-    List<String> WPT_KEYS = Arrays.asList(PT_ELE, PT_TIME, PT_MAGVAR, PT_GEOIDHEIGHT,
+    List<String> WPT_KEYS = Collections.unmodifiableList(Arrays.asList(PT_ELE, PT_TIME, PT_MAGVAR, PT_GEOIDHEIGHT,
             GPX_NAME, GPX_CMT, GPX_DESC, GPX_SRC, META_LINKS, PT_SYM, PT_TYPE,
-            PT_FIX, PT_SAT, PT_HDOP, PT_VDOP, PT_PDOP, PT_AGEOFDGPSDATA, PT_DGPSID, META_EXTENSIONS);
+            PT_FIX, PT_SAT, PT_HDOP, PT_VDOP, PT_PDOP, PT_AGEOFDGPSDATA, PT_DGPSID, META_EXTENSIONS));
 
     /**
      * Ordered list of all possible route and track keys.
      */
-    List<String> RTE_TRK_KEYS = Arrays.asList(
-            GPX_NAME, GPX_CMT, GPX_DESC, GPX_SRC, META_LINKS, "number", PT_TYPE, META_EXTENSIONS);
+    List<String> RTE_TRK_KEYS = Collections.unmodifiableList(Arrays.asList(
+            GPX_NAME, GPX_CMT, GPX_DESC, GPX_SRC, META_LINKS, "number", PT_TYPE, META_EXTENSIONS));
 
     /**
      * Possible fix values.
      */
-    Collection<String> FIX_VALUES = Arrays.asList("none", "2d", "3d", "dgps", "pps");
+    Collection<String> FIX_VALUES = Collections.unmodifiableList(Arrays.asList("none", "2d", "3d", "dgps", "pps"));
 }