diff --git a/src/java/com/threerings/miso/client/MisoScenePanel.java b/src/java/com/threerings/miso/client/MisoScenePanel.java
index 44212399..ecf5cd7f 100644
--- a/src/java/com/threerings/miso/client/MisoScenePanel.java
+++ b/src/java/com/threerings/miso/client/MisoScenePanel.java
@@ -47,6 +47,7 @@ import java.util.List;
 import java.util.Map;
 import java.util.Set;
 import java.util.WeakHashMap;
+import java.util.concurrent.ConcurrentHashMap;
 
 import javax.swing.Icon;
 import javax.swing.JFrame;
@@ -1532,7 +1533,8 @@ public class MisoScenePanel extends VirtualMediaPanel
     protected RethinkOp _rethinkOp;
 
     /** Contains our scene blocks. See {@link #getBlock} for details. */
-    protected HashIntMap<SceneBlock> _blocks = new HashIntMap<SceneBlock>();
+    protected ConcurrentHashMap<Integer, SceneBlock> _blocks =
+        new ConcurrentHashMap<Integer, SceneBlock>();
 
     /** A count of blocks in the process of being resolved. */
     protected int _pendingBlocks;
diff --git a/src/java/com/threerings/miso/client/SceneBlock.java b/src/java/com/threerings/miso/client/SceneBlock.java
index 7ddadd43..20c084dd 100644
--- a/src/java/com/threerings/miso/client/SceneBlock.java
+++ b/src/java/com/threerings/miso/client/SceneBlock.java
@@ -33,7 +33,6 @@ import java.awt.Rectangle;
 import com.google.common.collect.Lists;
 
 import com.samskivert.util.ArrayUtil;
-import com.samskivert.util.IntMap;
 import com.samskivert.util.StringUtil;
 
 import com.threerings.media.tile.NoSuchTileSetException;
@@ -513,7 +512,7 @@ public class SceneBlock
      * Links this block to its neighbors; informs neighboring blocks of
      * object coverage.
      */
-    protected void update (IntMap<SceneBlock> blocks)
+    protected void update (Map<Integer, SceneBlock> blocks)
     {
         boolean recover = false;
 
@@ -557,7 +556,7 @@ public class SceneBlock
     /**
      * Sets the footprint of this object tile
      */
-    protected void setCovered (IntMap<SceneBlock> blocks, SceneObject scobj)
+    protected void setCovered (Map<Integer, SceneBlock> blocks, SceneObject scobj)
     {
         int endx = scobj.info.x - scobj.tile.getBaseWidth() + 1;
         int endy = scobj.info.y - scobj.tile.getBaseHeight() + 1;