diff --git a/src/main/java/fr/moribus/imageonmap/image/ImageRendererExecutor.java b/src/main/java/fr/moribus/imageonmap/image/ImageRendererExecutor.java
index 3fe780b..8a5fec9 100644
--- a/src/main/java/fr/moribus/imageonmap/image/ImageRendererExecutor.java
+++ b/src/main/java/fr/moribus/imageonmap/image/ImageRendererExecutor.java
@@ -86,31 +86,32 @@ public class ImageRendererExecutor extends Worker
     
     static private ImageMap RenderSingle(final BufferedImage image, final UUID playerUUID) throws Throwable
     {
-        final short mapID = instance.submitToMainThread(new Callable<Short>()
+        Future<Short> futureMapID = instance.submitToMainThread(new Callable<Short>()
         {
             @Override
             public Short call() throws Exception
             {
                 return MapManager.getNewMapsIds(1)[0];
             }
-        }).get();
+        });
         
         final BufferedImage finalImage = ResizeImage(image, ImageMap.WIDTH, ImageMap.HEIGHT);
         
+        final short mapID = futureMapID.get();
         ImageIOExecutor.saveImage(mapID, finalImage);
         
-        final ImageMap newMap = instance.submitToMainThread(new Callable<ImageMap>()
+        instance.submitToMainThread(new Callable<Void>()
         {
             @Override
-            public ImageMap call() throws Exception
+            public Void call() throws Exception
             {
                 Renderer.installRenderer(finalImage, mapID);
-                return MapManager.createMap(playerUUID, mapID);
+                return null;
             }
 
-        }).get();
+        });
         
-        return newMap;
+        return MapManager.createMap(playerUUID, mapID);
     }
     
     static private ImageMap RenderPoster(final BufferedImage image, final UUID playerUUID) throws Throwable
@@ -133,18 +134,18 @@ public class ImageRendererExecutor extends Worker
         
         ImageIOExecutor.saveImage(mapsIDs, poster);
         
-        final ImageMap newMap = instance.submitToMainThread(new Callable<ImageMap>()
+        instance.submitToMainThread(new Callable<Void>()
         {
             @Override
-            public ImageMap call() throws Exception
+            public Void call() throws Exception
             {
                 Renderer.installRenderer(poster, mapsIDs);
-                return MapManager.createMap(poster, playerUUID, mapsIDs);
+                return null;
             }
 
-        }).get();
+        });
         
-        return newMap;
+        return MapManager.createMap(poster, playerUUID, mapsIDs);
     }
     
     static private BufferedImage ResizeImage(BufferedImage source, int destinationW, int destinationH)
diff --git a/src/main/java/fr/moribus/imageonmap/map/ImageMap.java b/src/main/java/fr/moribus/imageonmap/map/ImageMap.java
index 143bdb4..d6457aa 100644
--- a/src/main/java/fr/moribus/imageonmap/map/ImageMap.java
+++ b/src/main/java/fr/moribus/imageonmap/map/ImageMap.java
@@ -119,9 +119,9 @@ public abstract class ImageMap implements ConfigurationSerializable
     public Map<String, Object> serialize()
     {
         Map<String, Object> map = new HashMap<String, Object>();
-        map.put("id", id);
+        map.put("id", getId());
         map.put("type", mapType.toString());
-        map.put("name", name);
+        map.put("name", getName());
         this.postSerialize(map);
         return map;
     }
@@ -153,17 +153,17 @@ public abstract class ImageMap implements ConfigurationSerializable
         return userUUID;
     }
 
-    public String getName()
+    public synchronized String getName()
     {
         return name;
     }
     
-    public String getId()
+    public synchronized String getId()
     {
         return id;
     }
 
-    public void rename(String id, String name)
+    public synchronized void rename(String id, String name)
     {
         this.id = id;
         this.name = name;
@@ -171,8 +171,7 @@ public abstract class ImageMap implements ConfigurationSerializable
     
     public void rename(String name)
     {
-        if(this.name.equals(name)) return;
-        this.id = MapManager.getNextAvailableMapID(name, userUUID);
-        this.name = name;
+        if(getName().equals(name)) return;
+        rename(MapManager.getNextAvailableMapID(name, getUserUUID()), name);
     }
 }
diff --git a/src/main/java/fr/moribus/imageonmap/map/PlayerMapStore.java b/src/main/java/fr/moribus/imageonmap/map/PlayerMapStore.java
index d964d98..ab56c52 100644
--- a/src/main/java/fr/moribus/imageonmap/map/PlayerMapStore.java
+++ b/src/main/java/fr/moribus/imageonmap/map/PlayerMapStore.java
@@ -45,7 +45,7 @@ public class PlayerMapStore implements ConfigurationSerializable
         this.playerUUID = playerUUID;
     }
     
-    public boolean managesMap(short mapID)
+    public synchronized boolean managesMap(short mapID)
     {
         for(ImageMap map : mapList)
         {
@@ -54,7 +54,7 @@ public class PlayerMapStore implements ConfigurationSerializable
         return false;
     }
     
-    public boolean managesMap(ItemStack item)
+    public synchronized boolean managesMap(ItemStack item)
     {
         for(ImageMap map : mapList)
         {
@@ -63,19 +63,19 @@ public class PlayerMapStore implements ConfigurationSerializable
         return false;
     }
     
-    public void addMap(ImageMap map)
+    public synchronized void addMap(ImageMap map)
     {
         mapList.add(map);
         notifyModification();
     }
     
-    public void deleteMap(ImageMap map)
+    public synchronized void deleteMap(ImageMap map)
     {
         mapList.remove(map);
         notifyModification();
     }
     
-    public boolean mapExists(String id)
+    public synchronized boolean mapExists(String id)
     {
         for(ImageMap map : mapList)
         {
@@ -98,12 +98,12 @@ public class PlayerMapStore implements ConfigurationSerializable
         return mapId + "-" + id;
     }
     
-    public List<ImageMap> getMapList()
+    public synchronized List<ImageMap> getMapList()
     {
         return new ArrayList(mapList);
     }
     
-    public ImageMap getMap(String mapId)
+    public synchronized ImageMap getMap(String mapId)
     {
         for(ImageMap map : mapList)
         {
@@ -120,12 +120,12 @@ public class PlayerMapStore implements ConfigurationSerializable
         return playerUUID;
     }
     
-    public boolean isModified()
+    public synchronized boolean isModified()
     {
         return modified;
     }
     
-    public void notifyModification()
+    public synchronized void notifyModification()
     {
         this.modified = true;
     }
@@ -137,7 +137,7 @@ public class PlayerMapStore implements ConfigurationSerializable
     {
         Map<String, Object> map = new HashMap<String, Object>();
         ArrayList<Map> list = new ArrayList<Map>();
-        synchronized(mapList)
+        synchronized(this)
         {
             for(ImageMap tMap : mapList)
             {
@@ -153,18 +153,17 @@ public class PlayerMapStore implements ConfigurationSerializable
         if(section == null) return;
         List<Map<String, Object>> list = (List<Map<String, Object>>) section.getList("mapList");
         if(list == null) return;
-        synchronized(mapList)
+        
+        for(Map<String, Object> tMap : list)
         {
-            for(Map<String, Object> tMap : list)
+            try
             {
-                try
-                {
-                    mapList.add(ImageMap.fromConfig(tMap, playerUUID));
-                }
-                catch(InvalidConfigurationException ex)
-                {
-                    PluginLogger.LogWarning("Could not load map data : " + ex.getMessage());
-                }
+                ImageMap newMap = ImageMap.fromConfig(tMap, playerUUID);
+                synchronized(this) {mapList.add(newMap);}
+            }
+            catch(InvalidConfigurationException ex)
+            {
+                PluginLogger.LogWarning("Could not load map data : " + ex.getMessage());
             }
         }
     }
@@ -205,6 +204,6 @@ public class PlayerMapStore implements ConfigurationSerializable
             PluginLogger.LogError("Could not save maps file for player " + playerUUID.toString(), ex);
         }
         PluginLogger.LogInfo("Saving maps file for " + playerUUID.toString());
-        modified = false;
+        synchronized(this) {modified = false;}
     }
 }
diff --git a/src/main/java/fr/moribus/imageonmap/map/PosterMap.java b/src/main/java/fr/moribus/imageonmap/map/PosterMap.java
index f99b544..daee3c8 100644
--- a/src/main/java/fr/moribus/imageonmap/map/PosterMap.java
+++ b/src/main/java/fr/moribus/imageonmap/map/PosterMap.java
@@ -25,9 +25,9 @@ import org.bukkit.configuration.InvalidConfigurationException;
 
 public class PosterMap extends ImageMap
 {
-    protected short[] mapsIDs;
-    protected int columnCount;
-    protected int rowCount;
+    protected final short[] mapsIDs;
+    protected final int columnCount;
+    protected final int rowCount;
     
     public PosterMap(UUID userUUID, short[] mapsIDs, int columnCount, int rowCount)
     {
diff --git a/src/main/java/fr/moribus/imageonmap/map/SingleMap.java b/src/main/java/fr/moribus/imageonmap/map/SingleMap.java
index 18e4bd0..f384a51 100644
--- a/src/main/java/fr/moribus/imageonmap/map/SingleMap.java
+++ b/src/main/java/fr/moribus/imageonmap/map/SingleMap.java
@@ -24,7 +24,7 @@ import org.bukkit.configuration.InvalidConfigurationException;
 
 public class SingleMap extends ImageMap
 {
-    protected short mapID;
+    protected final short mapID;
     
     public SingleMap(UUID ownerUUID, short mapID)
     {