diff --git a/src/java/com/threerings/whirled/spot/data/SpotCodes.java b/src/java/com/threerings/whirled/spot/data/SpotCodes.java
index 6d37c4555..bed5dd514 100644
--- a/src/java/com/threerings/whirled/spot/data/SpotCodes.java
+++ b/src/java/com/threerings/whirled/spot/data/SpotCodes.java
@@ -1,5 +1,5 @@
 //
-// $Id: SpotCodes.java,v 1.3 2002/08/14 19:07:58 mdb Exp $
+// $Id: SpotCodes.java,v 1.4 2003/03/26 22:34:24 mdb Exp $
 
 package com.threerings.whirled.spot.data;
 
@@ -21,6 +21,10 @@ public interface SpotCodes extends ChatCodes, SceneCodes
      * generated by a failed changeLoc request. */
     public static final String LOCATION_OCCUPIED = "m.location_occupied";
 
+    /** An error code indicating that a location is not valid. Usually
+     * generated by a failed changeLoc request. */
+    public static final String INVALID_LOCATION = "m.invalid_location";
+
     /** The chat type code with which we register our cluster auxiliary
      * chat objects. Chat display implementations should interpret chat
      * messages with this type accordingly. */
diff --git a/src/java/com/threerings/whirled/spot/server/SpotSceneManager.java b/src/java/com/threerings/whirled/spot/server/SpotSceneManager.java
index 1d4cd38a2..19486c908 100644
--- a/src/java/com/threerings/whirled/spot/server/SpotSceneManager.java
+++ b/src/java/com/threerings/whirled/spot/server/SpotSceneManager.java
@@ -1,5 +1,5 @@
 //
-// $Id: SpotSceneManager.java,v 1.32 2003/03/26 18:18:29 mdb Exp $
+// $Id: SpotSceneManager.java,v 1.33 2003/03/26 22:34:24 mdb Exp $
 
 package com.threerings.whirled.spot.server;
 
@@ -183,7 +183,10 @@ public class SpotSceneManager extends SceneManager
             throw new InvocationException(INTERNAL_ERROR);
         }
 
-        // TODO: make sure the location isn't too close to another user
+        // let our derived classes decide if this is an OK place to stand
+        if (!validateLocation(source, loc)) {
+            throw new InvocationException(INTERNAL_ERROR);
+        }
 
         // update the user's location information in the scene which will
         // indicate to the client that their avatar should be moved from
@@ -194,6 +197,17 @@ public class SpotSceneManager extends SceneManager
         removeFromCluster(source.getOid());
     }
 
+    /**
+     * Derived classes can override this method and validate that the
+     * specified body can stand in the requested location. The default
+     * implementation returns <code>true</code> in all circumstances;
+     * stand where ye may!
+     */
+    protected boolean validateLocation (BodyObject source, Location loc)
+    {
+        return true;
+    }
+
     /**
      * Updates the location of the specified body.
      */