diff --git a/src/as/com/threerings/util/ArrayUtil.as b/src/as/com/threerings/util/ArrayUtil.as
index 8dfa5f029..af840f122 100644
--- a/src/as/com/threerings/util/ArrayUtil.as
+++ b/src/as/com/threerings/util/ArrayUtil.as
@@ -32,12 +32,20 @@ public class ArrayUtil
 {
     /**
      * Sort the specified array according to natural order- all elements
-     * must implement Comparable.
+     * must implement Comparable or be null.
      */
     public static function sort (arr :Array) :void
     {
         arr.sort(function (obj1 :Object, obj2 :Object) :int {
-            return Comparable(obj1).compareTo(obj2);
+            if (obj1 == obj2) { // same object or both null
+                return 0;
+            } else if (obj1 == null) {
+                return -1;
+            } else if (obj2 == null) {
+                return 1;
+            } else {
+                return Comparable(obj1).compareTo(obj2);
+            }
         });
     }
 
diff --git a/src/as/com/threerings/util/SortedHashMap.as b/src/as/com/threerings/util/SortedHashMap.as
index 0edf7bd34..4e41f5eeb 100644
--- a/src/as/com/threerings/util/SortedHashMap.as
+++ b/src/as/com/threerings/util/SortedHashMap.as
@@ -88,6 +88,9 @@ public class SortedHashMap extends HashMap
     protected function validateKey (key :Object) :void
         // throws ArgumentError
     {
+        if (key == null) {
+            return;
+        }
         switch (_keyType) {
         case COMPARABLE_KEYS:
             if (key is Comparable) {