diff --git a/src/api/java/appeng/api/storage/ICellRegistry.java b/src/api/java/appeng/api/storage/ICellRegistry.java
index a692e0044..ad3563bc0 100644
--- a/src/api/java/appeng/api/storage/ICellRegistry.java
+++ b/src/api/java/appeng/api/storage/ICellRegistry.java
@@ -24,7 +24,11 @@
 package appeng.api.storage;
 
 
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+
 import net.minecraft.item.ItemStack;
+import net.minecraftforge.fml.common.event.FMLInitializationEvent;
 
 import appeng.api.IAppEngApi;
 import appeng.api.storage.data.IAEStack;
@@ -42,9 +46,12 @@ public interface ICellRegistry
 	/**
 	 * Register a new handler.
 	 *
+	 * Never be call before {@link FMLInitializationEvent} was handled by AE2.
+	 * Will throw an exception otherwise.
+	 *
 	 * @param handler cell handler
 	 */
-	void addCellHandler( ICellHandler handler );
+	void addCellHandler( @Nonnull ICellHandler handler );
 
 	/**
 	 * return true, if you can get a InventoryHandler for the item passed.
@@ -63,6 +70,7 @@ public interface ICellRegistry
 	 *
 	 * @return the handler registered for this item type.
 	 */
+	@Nullable
 	ICellHandler getHandler( ItemStack is );
 
 	/**
@@ -74,5 +82,6 @@ public interface ICellRegistry
 	 *
 	 * @return new IMEInventoryHandler, or null if there isn't one.
 	 */
+	@Nullable
 	<T extends IAEStack<T>> IMEInventoryHandler<T> getCellInventory( ItemStack is, ISaveProvider host, IStorageChannel<T> chan );
 }
\ No newline at end of file
diff --git a/src/main/java/appeng/core/features/registries/cell/BasicCellHandler.java b/src/main/java/appeng/core/features/registries/cell/BasicCellHandler.java
index e386cdd26..063ba963c 100644
--- a/src/main/java/appeng/core/features/registries/cell/BasicCellHandler.java
+++ b/src/main/java/appeng/core/features/registries/cell/BasicCellHandler.java
@@ -41,7 +41,7 @@ import appeng.me.storage.CellInventoryHandler;
 import appeng.util.Platform;
 
 
-public class BasicCellHandler implements ICellHandler
+public final class BasicCellHandler implements ICellHandler
 {
 
 	@Override
diff --git a/src/main/java/appeng/core/features/registries/cell/CellRegistry.java b/src/main/java/appeng/core/features/registries/cell/CellRegistry.java
index dd1726fed..0bd4f0c1f 100644
--- a/src/main/java/appeng/core/features/registries/cell/CellRegistry.java
+++ b/src/main/java/appeng/core/features/registries/cell/CellRegistry.java
@@ -22,6 +22,9 @@ package appeng.core.features.registries.cell;
 import java.util.ArrayList;
 import java.util.List;
 
+import com.google.common.base.Preconditions;
+import com.google.common.base.Verify;
+
 import net.minecraft.item.ItemStack;
 
 import appeng.api.storage.ICellHandler;
@@ -43,12 +46,15 @@ public class CellRegistry implements ICellRegistry
 	}
 
 	@Override
-	public void addCellHandler( final ICellHandler h )
+	public void addCellHandler( final ICellHandler handler )
 	{
-		if( h != null )
-		{
-			this.handlers.add( h );
-		}
+		Preconditions.checkNotNull( handler, "Called before FMLInitializationEvent." );
+		Preconditions.checkArgument( !this.handlers.contains( handler ), "Tried to register the same handler instance twice." );
+
+		this.handlers.add( handler );
+
+		// Verify that the first entry is always our own handler.
+		Verify.verify( this.handlers.get( 0 ) instanceof BasicCellHandler );
 	}
 
 	@Override
diff --git a/src/main/java/appeng/core/features/registries/cell/CreativeCellHandler.java b/src/main/java/appeng/core/features/registries/cell/CreativeCellHandler.java
index 414950086..8c4b4168b 100644
--- a/src/main/java/appeng/core/features/registries/cell/CreativeCellHandler.java
+++ b/src/main/java/appeng/core/features/registries/cell/CreativeCellHandler.java
@@ -38,7 +38,7 @@ import appeng.me.storage.CreativeCellInventory;
 import appeng.util.Platform;
 
 
-public class CreativeCellHandler implements ICellHandler
+public final class CreativeCellHandler implements ICellHandler
 {
 
 	@Override