diff --git a/src/as/com/threerings/ezgame/EZGameControl.as b/src/as/com/threerings/ezgame/EZGameControl.as
index fb249ada..394905a9 100644
--- a/src/as/com/threerings/ezgame/EZGameControl.as
+++ b/src/as/com/threerings/ezgame/EZGameControl.as
@@ -153,11 +153,24 @@ public class EZGameControl extends EventDispatcher
     }
 
     /**
-     * Set a property that will be distributed. 
+     * Set a property that will be distributed.
      */
     public function set (propName :String, value :Object, index :int = -1) :void
     {
-        callEZCode("setProperty_v1", propName, value, index);
+        callEZCode("setProperty_v2", propName, value, index, false);
+    }
+
+    /**
+     * Set a property that will be distributed, but only if it was null before.
+     *
+     * The operation is 'atomic', in the sense that testing and setting take place
+     * during the same server event. In comparison, a separate 'get' followed by
+     * a 'set' operation would involve two events with two network round-trips,
+     * and no guarantee that the value won't change between the events.
+     */
+    public function testAndSet (propName :String, value :Object, index :int = -1) :void
+    {
+        callEZCode("setProperty_v2", propName, value, index, true);
     }
 
     /**
diff --git a/src/as/com/threerings/ezgame/client/EZGameService.as b/src/as/com/threerings/ezgame/client/EZGameService.as
index 329e572c..63455ace 100644
--- a/src/as/com/threerings/ezgame/client/EZGameService.as
+++ b/src/as/com/threerings/ezgame/client/EZGameService.as
@@ -67,7 +67,7 @@ public interface EZGameService extends InvocationService
     function setCookie (arg1 :Client, arg2 :ByteArray, arg3 :InvocationService_InvocationListener) :void;
 
     // from Java interface EZGameService
-    function setProperty (arg1 :Client, arg2 :String, arg3 :Object, arg4 :int, arg5 :InvocationService_InvocationListener) :void;
+    function setProperty (arg1 :Client, arg2 :String, arg3 :Object, arg4 :int, arg5 :Boolean, arg6 :InvocationService_InvocationListener) :void;
 
     // from Java interface EZGameService
     function setTicker (arg1 :Client, arg2 :String, arg3 :int, arg4 :InvocationService_InvocationListener) :void;
diff --git a/src/as/com/threerings/ezgame/client/GameControlBackend.as b/src/as/com/threerings/ezgame/client/GameControlBackend.as
index ef77b841..fe30b550 100644
--- a/src/as/com/threerings/ezgame/client/GameControlBackend.as
+++ b/src/as/com/threerings/ezgame/client/GameControlBackend.as
@@ -72,7 +72,7 @@ public class GameControlBackend
     {
         _ctx = ctx;
         _ezObj = ezObj;
-        _gameData = new GameData(setProperty_v1, _ezObj.getUserProps());
+        _gameData = new GameData(setProperty_v2, _ezObj.getUserProps());
 
         _ezObj.addListener(this);
         _ctx.getClient().getClientObject().addListener(_userListener);
@@ -136,7 +136,7 @@ public class GameControlBackend
         o["gameData"] = _gameData;
 
         // functions
-        o["setProperty_v1"] = setProperty_v1;
+        o["setProperty_v2"] = setProperty_v2;
         o["mergeCollection_v1"] = mergeCollection_v1;
         o["setTicker_v1"] = setTicker_v1;
         o["sendChat_v1"] = sendChat_v1;
@@ -163,18 +163,18 @@ public class GameControlBackend
         o["getPlayers_v1"] = getPlayers_v1;
     }
 
-    public function setProperty_v1 (
-        propName :String, value :Object, index :int) :void
+    public function setProperty_v2 (
+        propName :String, value :Object, index :int, testAndSet :Boolean) :void
     {
         validatePropertyChange(propName, value, index);
 
         var encoded :Object = EZObjectMarshaller.encode(value, (index == -1));
         _ezObj.ezGameService.setProperty(
-            _ctx.getClient(), propName, encoded, index,
+            _ctx.getClient(), propName, encoded, index, testAndSet,
             createLoggingConfirmListener("setProperty"));
 
         // set it immediately in the game object
-        _ezObj.applyPropertySet(propName, value, index);
+        _ezObj.applyPropertySet(propName, value, index, testAndSet);
     }
 
     public function mergeCollection_v1 (
diff --git a/src/as/com/threerings/ezgame/client/GameData.as b/src/as/com/threerings/ezgame/client/GameData.as
index d408aec1..c6bd82e8 100644
--- a/src/as/com/threerings/ezgame/client/GameData.as
+++ b/src/as/com/threerings/ezgame/client/GameData.as
@@ -67,7 +67,7 @@ public class GameData extends Proxy
 
     override flash_proxy function setProperty (propName :*, value :*) :void
     {
-        _propSetFn(String(propName), value, -1);
+        _propSetFn(String(propName), value, -1, false);
     }
 
     override flash_proxy function deleteProperty (propName :*) :Boolean
diff --git a/src/as/com/threerings/ezgame/data/EZGameMarshaller.as b/src/as/com/threerings/ezgame/data/EZGameMarshaller.as
index be50f3b1..306ef887 100644
--- a/src/as/com/threerings/ezgame/data/EZGameMarshaller.as
+++ b/src/as/com/threerings/ezgame/data/EZGameMarshaller.as
@@ -178,12 +178,12 @@ public class EZGameMarshaller extends InvocationMarshaller
     public static const SET_PROPERTY :int = 11;
 
     // from interface EZGameService
-    public function setProperty (arg1 :Client, arg2 :String, arg3 :Object, arg4 :int, arg5 :InvocationService_InvocationListener) :void
+    public function setProperty (arg1 :Client, arg2 :String, arg3 :Object, arg4 :int, arg5 :Boolean, arg6 :InvocationService_InvocationListener) :void
     {
-        var listener5 :InvocationMarshaller_ListenerMarshaller = new InvocationMarshaller_ListenerMarshaller();
-        listener5.listener = arg5;
+        var listener6 :InvocationMarshaller_ListenerMarshaller = new InvocationMarshaller_ListenerMarshaller();
+        listener6.listener = arg6;
         sendRequest(arg1, SET_PROPERTY, [
-            arg2, arg3, Integer.valueOf(arg4), listener5
+            arg2, arg3, Integer.valueOf(arg4), langBoolean.valueOf(arg5), listener6
         ]);
     }
 
diff --git a/src/as/com/threerings/ezgame/data/EZGameObject.as b/src/as/com/threerings/ezgame/data/EZGameObject.as
index b5757b3a..8ebfc41f 100644
--- a/src/as/com/threerings/ezgame/data/EZGameObject.as
+++ b/src/as/com/threerings/ezgame/data/EZGameObject.as
@@ -98,26 +98,30 @@ public class EZGameObject extends GameObject
      * @return the old value
      */
     public function applyPropertySet (
-        propName :String, value :Object, index :int) :Object
+        propName :String, value :Object, index :int, testAndSet :Boolean)
+        :Object
     {
         var oldValue :Object = _props[propName];
-        if (index >= 0) {
-            // set an array element
-            var arr :Array = (oldValue as Array);
-            if (arr == null) {
-                arr = [];
-                _props[propName] = arr;
+        if ((testAndSet && oldValue == null) || ! testAndSet)
+        {
+            if (index >= 0) {
+                // set an array element
+                var arr :Array = (oldValue as Array);
+                if (arr == null) {
+                    arr = [];
+                    _props[propName] = arr;
+                }
+                oldValue = arr[index];
+                arr[index] = value;
+                
+            } else if (value != null) {
+                // normal property set
+                _props[propName] = value;
+                
+            } else {
+                // remove a property
+                delete _props[propName];
             }
-            oldValue = arr[index];
-            arr[index] = value;
-
-        } else if (value != null) {
-            // normal property set
-            _props[propName] = value;
-
-        } else {
-            // remove a property
-            delete _props[propName];
         }
         return oldValue;
     }
diff --git a/src/as/com/threerings/ezgame/data/PropertySetEvent.as b/src/as/com/threerings/ezgame/data/PropertySetEvent.as
index b9943c73..bd491716 100644
--- a/src/as/com/threerings/ezgame/data/PropertySetEvent.as
+++ b/src/as/com/threerings/ezgame/data/PropertySetEvent.as
@@ -35,7 +35,7 @@ public class PropertySetEvent extends NamedEvent
     override public function applyToObject (target :DObject) :Boolean
     {
         _oldValue =
-            EZGameObject(target).applyPropertySet(_name, _data, _index);
+            EZGameObject(target).applyPropertySet(_name, _data, _index, _testAndSet);
         return true;
     }
 
@@ -69,6 +69,7 @@ public class PropertySetEvent extends NamedEvent
         super.readObject(ins);
         _index = ins.readInt();
         _data = EZObjectMarshaller.decode(ins.readObject());
+        _testAndSet = ins.readBoolean();
     }
 
     // from interface Streamable
@@ -77,6 +78,7 @@ public class PropertySetEvent extends NamedEvent
         super.writeObject(out);
         out.writeInt(_index);
         out.writeObject(_data);
+        out.writeBoolean(_testAndSet);
     }
 
     override protected function notifyListener (listener :Object) :void
@@ -99,6 +101,9 @@ public class PropertySetEvent extends NamedEvent
     /** The client-side data that is assigned to this property. */
     protected var _data :Object;
 
+    /** When true, the property will only be set if its previous value was null. */
+    protected var _testAndSet :Boolean;
+
     /** The old value. */
     protected var _oldValue :Object;
 }
diff --git a/src/java/com/threerings/ezgame/EZGame.java b/src/java/com/threerings/ezgame/EZGame.java
index af2cbc1d..fa2ad354 100644
--- a/src/java/com/threerings/ezgame/EZGame.java
+++ b/src/java/com/threerings/ezgame/EZGame.java
@@ -27,6 +27,16 @@ public interface EZGame
      */
     public void set (String propName, Object value, int index);
 
+    /**
+     * Set a property that will be distributed. 
+     */
+    public void set (String propName, Object value, boolean testAndSet);
+
+    /**
+     * Set a property that will be distributed. 
+     */
+    public void set (String propName, Object value, int index, boolean testAndSet);
+
     /**
      * Register an object to receive whatever events it should receive,
      * based on which event listeners it implements. Note that it is not
diff --git a/src/java/com/threerings/ezgame/client/EZGameService.java b/src/java/com/threerings/ezgame/client/EZGameService.java
index c2de38d4..ea18d981 100644
--- a/src/java/com/threerings/ezgame/client/EZGameService.java
+++ b/src/java/com/threerings/ezgame/client/EZGameService.java
@@ -20,7 +20,7 @@ public interface EZGameService extends InvocationService
      */
     public void setProperty (
         Client client, String propName, Object value, int index,
-        InvocationListener listener);
+        boolean testAndSet, InvocationListener listener);
 
     /**
      * Request to end the turn, possibly futzing the next turn holder unless
diff --git a/src/java/com/threerings/ezgame/client/GameObjectImpl.java b/src/java/com/threerings/ezgame/client/GameObjectImpl.java
index ccdfdc39..60d2e8fb 100644
--- a/src/java/com/threerings/ezgame/client/GameObjectImpl.java
+++ b/src/java/com/threerings/ezgame/client/GameObjectImpl.java
@@ -61,22 +61,34 @@ public class GameObjectImpl
     // from EZGame
     public void set (String propName, Object value)
     {
-        set(propName, value, -1);
+        set(propName, value, -1, false);
+    }
+
+    // from EZGame
+    public void set (String propName, Object value, boolean testAndSet)
+    {
+        set(propName, value, -1, testAndSet);
     }
 
     // from EZGame
     public void set (String propName, Object value, int index)
+    {
+        set(propName, value, index, false);
+    }
+    
+    // from EZGame
+    public void set (String propName, Object value, int index, boolean testAndSet)
     {
         validatePropertyChange(propName, value, -1);
 
         Object encoded = EZObjectMarshaller.encode(value);
         Object reconstituted = EZObjectMarshaller.decode(encoded);
         _ezObj.ezGameService.setProperty(
-            _ctx.getClient(), propName, encoded, index,
+            _ctx.getClient(), propName, encoded, index, testAndSet,
             createLoggingListener("setProperty"));
 
         // set it immediately in the game object
-        _ezObj.applyPropertySet(propName, reconstituted, index);
+        _ezObj.applyPropertySet(propName, reconstituted, index, testAndSet);
     }
 
     // from EZGame
diff --git a/src/java/com/threerings/ezgame/data/EZGameMarshaller.java b/src/java/com/threerings/ezgame/data/EZGameMarshaller.java
index 000f259b..20ac56d2 100644
--- a/src/java/com/threerings/ezgame/data/EZGameMarshaller.java
+++ b/src/java/com/threerings/ezgame/data/EZGameMarshaller.java
@@ -171,12 +171,12 @@ public class EZGameMarshaller extends InvocationMarshaller
     public static final int SET_PROPERTY = 11;
 
     // from interface EZGameService
-    public void setProperty (Client arg1, String arg2, Object arg3, int arg4, InvocationService.InvocationListener arg5)
+    public void setProperty (Client arg1, String arg2, Object arg3, int arg4, boolean arg5, InvocationService.InvocationListener arg6)
     {
-        ListenerMarshaller listener5 = new ListenerMarshaller();
-        listener5.listener = arg5;
+        ListenerMarshaller listener6 = new ListenerMarshaller();
+        listener6.listener = arg6;
         sendRequest(arg1, SET_PROPERTY, new Object[] {
-            arg2, arg3, Integer.valueOf(arg4), listener5
+            arg2, arg3, Integer.valueOf(arg4), Boolean.valueOf(arg5), listener6
         });
     }
 
diff --git a/src/java/com/threerings/ezgame/data/EZGameObject.java b/src/java/com/threerings/ezgame/data/EZGameObject.java
index f379e82b..abd70686 100644
--- a/src/java/com/threerings/ezgame/data/EZGameObject.java
+++ b/src/java/com/threerings/ezgame/data/EZGameObject.java
@@ -85,46 +85,50 @@ public class EZGameObject extends GameObject
     /**
      * Called by PropertySetEvent to effect the property update.
      */
-    public Object applyPropertySet (String propName, Object data, int index)
+    public Object applyPropertySet (
+        String propName, Object data, int index, boolean testAndSet)
     {
         Object oldValue = _props.get(propName);
-        if (index >= 0) {
-            if (isOnServer()) {
-                byte[][] arr = (oldValue instanceof byte[][])
-                    ? (byte[][]) oldValue : null;
-                if (arr == null || arr.length <= index) {
-                    // TODO: in case a user sets element 0 and element 90000,
-                    // we might want to store elements in a hash
-                    byte[][] newArr = new byte[index + 1][];
-                    if (arr != null) {
-                        System.arraycopy(arr, 0, newArr, 0, arr.length);
+        if ((testAndSet && oldValue == null) || ! testAndSet)
+        {
+            if (index >= 0) {
+                if (isOnServer()) {
+                    byte[][] arr = (oldValue instanceof byte[][])
+                        ? (byte[][]) oldValue : null;
+                    if (arr == null || arr.length <= index) {
+                        // TODO: in case a user sets element 0 and element 90000,
+                        // we might want to store elements in a hash
+                        byte[][] newArr = new byte[index + 1][];
+                        if (arr != null) {
+                            System.arraycopy(arr, 0, newArr, 0, arr.length);
+                        }
+                        _props.put(propName, newArr);
+                        arr = newArr;
                     }
-                    _props.put(propName, newArr);
-                    arr = newArr;
+                    oldValue = arr[index];
+                    arr[index] = (byte[]) data;
+
+                } else {
+                    Object[] arr = (oldValue instanceof Object[])
+                        ? (Object[]) oldValue : null;
+                    if (arr == null || arr.length <= index) {
+                        Object[] newArr = new Object[index + 1];
+                        if (arr != null) {
+                            System.arraycopy(arr, 0, newArr, 0, arr.length);
+                        }
+                        _props.put(propName, newArr);
+                        arr = newArr;
+                    }
+                    oldValue = arr[index];
+                    arr[index] = data;
                 }
-                oldValue = arr[index];
-                arr[index] = (byte[]) data;
+
+            } else if (data != null) {
+                _props.put(propName, data);
 
             } else {
-                Object[] arr = (oldValue instanceof Object[])
-                    ? (Object[]) oldValue : null;
-                if (arr == null || arr.length <= index) {
-                    Object[] newArr = new Object[index + 1];
-                    if (arr != null) {
-                        System.arraycopy(arr, 0, newArr, 0, arr.length);
-                    }
-                    _props.put(propName, newArr);
-                    arr = newArr;
-                }
-                oldValue = arr[index];
-                arr[index] = data;
+                _props.remove(propName);
             }
-
-        } else if (data != null) {
-            _props.put(propName, data);
-
-        } else {
-            _props.remove(propName);
         }
 
         return oldValue;
diff --git a/src/java/com/threerings/ezgame/data/PropertySetEvent.java b/src/java/com/threerings/ezgame/data/PropertySetEvent.java
index 92adcafd..52d5ca37 100644
--- a/src/java/com/threerings/ezgame/data/PropertySetEvent.java
+++ b/src/java/com/threerings/ezgame/data/PropertySetEvent.java
@@ -30,11 +30,12 @@ public class PropertySetEvent extends NamedEvent
      * Create a PropertySetEvent.
      */
     public PropertySetEvent (
-        int targetOid, String propName, Object value, int index)
+        int targetOid, String propName, Object value, int index, boolean testAndSet)
     {
         super(targetOid, propName);
         _data = value;
         _index = index;
+        _testAndSet = testAndSet;
     }
 
     /**
@@ -68,7 +69,7 @@ public class PropertySetEvent extends NamedEvent
         if (!ezObj.isOnServer()) {
             _data = EZObjectMarshaller.decode(_data);
         }
-        _oldValue = ezObj.applyPropertySet(_name, _data, _index);
+        _oldValue = ezObj.applyPropertySet(_name, _data, _index, _testAndSet);
         return true;
     }
 
@@ -94,6 +95,9 @@ public class PropertySetEvent extends NamedEvent
     /** The client-side data that is assigned to this property. */
     protected Object _data;
 
+    /** When true, the property will only be set if the old value was null. */
+    protected boolean _testAndSet;
+    
     /** The old value. */
     protected transient Object _oldValue;
 }
diff --git a/src/java/com/threerings/ezgame/server/DictionaryService.java b/src/java/com/threerings/ezgame/server/DictionaryService.java
index 3ff98eca..8349f08d 100644
--- a/src/java/com/threerings/ezgame/server/DictionaryService.java
+++ b/src/java/com/threerings/ezgame/server/DictionaryService.java
@@ -174,15 +174,6 @@ public class DictionaryService
     }
 
 
-    /**
-     * Obsolete init function. I'm keeping it around to prevent
-     * any automated build breakage between the upcoming Vilya checkin
-     * and the subsequent MSoy checkin. But this will go away real soon.
-     */
-    public static void init ()
-    {
-    }
-
     /**
      * Creates the singleton instance of the dictionary service.
      */
diff --git a/src/java/com/threerings/ezgame/server/EZGameDispatcher.java b/src/java/com/threerings/ezgame/server/EZGameDispatcher.java
index dc0b1ce3..00e6d2b1 100644
--- a/src/java/com/threerings/ezgame/server/EZGameDispatcher.java
+++ b/src/java/com/threerings/ezgame/server/EZGameDispatcher.java
@@ -129,7 +129,7 @@ public class EZGameDispatcher extends InvocationDispatcher
         case EZGameMarshaller.SET_PROPERTY:
             ((EZGameProvider)provider).setProperty(
                 source,
-                (String)args[0], (Object)args[1], ((Integer)args[2]).intValue(), (InvocationService.InvocationListener)args[3]
+                (String)args[0], (Object)args[1], ((Integer)args[2]).intValue(), ((Boolean)args[3]).booleanValue(), (InvocationService.InvocationListener)args[4]
             );
             return;
 
diff --git a/src/java/com/threerings/ezgame/server/EZGameManager.java b/src/java/com/threerings/ezgame/server/EZGameManager.java
index 8f455f19..28b12f61 100644
--- a/src/java/com/threerings/ezgame/server/EZGameManager.java
+++ b/src/java/com/threerings/ezgame/server/EZGameManager.java
@@ -127,11 +127,11 @@ public class EZGameManager extends GameManager
     // from EZGameProvider
     public void setProperty (
         ClientObject caller, String propName, Object data, int index,
-        InvocationService.InvocationListener listener)
+        boolean testAndSet, InvocationService.InvocationListener listener)
         throws InvocationException
     {
         validateUser(caller);
-        setProperty(propName, data, index);
+        setProperty(propName, data, index, testAndSet);
     }
 
     // from EZGameProvider
@@ -220,7 +220,7 @@ public class EZGameManager extends GameManager
                 }
 
                 if (playerId == 0) {
-                    setProperty(msgOrPropName, result, -1);
+                    setProperty(msgOrPropName, result, -1, false);
                     
                 } else {
                     sendPrivateMessage(playerId, msgOrPropName, result);
@@ -400,10 +400,12 @@ public class EZGameManager extends GameManager
     /**
      * Helper method to post a property set event.
      */
-    protected void setProperty (String propName, Object value, int index)
+    protected void setProperty (
+        String propName, Object value, int index, boolean testAndSet)
     {
         _gameObj.postEvent(
-            new PropertySetEvent(_gameObj.getOid(), propName, value, index));
+            new PropertySetEvent(
+                _gameObj.getOid(), propName, value, index, testAndSet));
     }
 
     /**
diff --git a/src/java/com/threerings/ezgame/server/EZGameProvider.java b/src/java/com/threerings/ezgame/server/EZGameProvider.java
index 06242815..38b22242 100644
--- a/src/java/com/threerings/ezgame/server/EZGameProvider.java
+++ b/src/java/com/threerings/ezgame/server/EZGameProvider.java
@@ -96,7 +96,7 @@ public interface EZGameProvider extends InvocationProvider
     /**
      * Handles a {@link EZGameService#setProperty} request.
      */
-    public void setProperty (ClientObject caller, String arg1, Object arg2, int arg3, InvocationService.InvocationListener arg4)
+    public void setProperty (ClientObject caller, String arg1, Object arg2, int arg3, boolean arg4, InvocationService.InvocationListener arg5)
         throws InvocationException;
 
     /**