diff --git a/src/main/scala/li/cil/oc/server/component/traits/InventoryTransfer.scala b/src/main/scala/li/cil/oc/server/component/traits/InventoryTransfer.scala
index 1989021bd..704ddcdbc 100644
--- a/src/main/scala/li/cil/oc/server/component/traits/InventoryTransfer.scala
+++ b/src/main/scala/li/cil/oc/server/component/traits/InventoryTransfer.scala
@@ -12,7 +12,7 @@ trait InventoryTransfer extends traits.WorldAware with traits.SideRestricted {
   // Return None on success, else Some("failure reason")
   def onTransferContents(): Option[String]
 
-  @Callback(doc = """function(sourceSide:number, sinkSide:number[, count:number[, sourceSlot:number, sinkSlot:number]]):number -- Transfer some items between two inventories.""")
+  @Callback(doc = """function(sourceSide:number, sinkSide:number[, count:number[, sourceSlot:number[, sinkSlot:number]]]):number -- Transfer some items between two inventories.""")
   def transferItem(context: Context, args: Arguments): Array[AnyRef] = {
     val sourceSide = checkSideForAction(args, 0)
     val sourcePos = position.offset(sourceSide)
@@ -26,9 +26,9 @@ trait InventoryTransfer extends traits.WorldAware with traits.SideRestricted {
       case _ =>
         if (args.count > 3) {
           val sourceSlot = args.checkSlot(InventoryUtils.inventoryAt(sourcePos).getOrElse(throw new IllegalArgumentException("no inventory")), 3)
-          val sinkSlot = args.checkSlot(InventoryUtils.inventoryAt(sinkPos).getOrElse(throw new IllegalArgumentException("no inventory")), 4)
+          val sinkSlot = args.optSlot(InventoryUtils.inventoryAt(sinkPos).getOrElse(throw new IllegalArgumentException("no inventory")), 4, -1)
 
-          result(InventoryUtils.transferBetweenInventoriesSlotsAt(sourcePos, sourceSide.getOpposite, sourceSlot, sinkPos, Option(sinkSide.getOpposite), sinkSlot, count))
+          result(InventoryUtils.transferBetweenInventoriesSlotsAt(sourcePos, sourceSide.getOpposite, sourceSlot, sinkPos, Option(sinkSide.getOpposite), if (sinkSlot < 0) None else Option(sinkSlot), count))
         }
         else result(InventoryUtils.transferBetweenInventoriesAt(sourcePos, sourceSide.getOpposite, sinkPos, Option(sinkSide.getOpposite), count))
     }
diff --git a/src/main/scala/li/cil/oc/util/InventoryUtils.scala b/src/main/scala/li/cil/oc/util/InventoryUtils.scala
index c2f21a5ec..f3ad8e898 100644
--- a/src/main/scala/li/cil/oc/util/InventoryUtils.scala
+++ b/src/main/scala/li/cil/oc/util/InventoryUtils.scala
@@ -249,9 +249,15 @@ object InventoryUtils {
   /**
    * Like <tt>transferBetweenInventories</tt> but moving between specific slots.
    */
-  def transferBetweenInventoriesSlots(source: IInventory, sourceSide: ForgeDirection, sourceSlot: Int, sink: IInventory, sinkSide: Option[ForgeDirection], sinkSlot: Int, limit: Int = 64) =
-    extractFromInventorySlot(
-      insertIntoInventorySlot(_, sink, sinkSide, sinkSlot, limit), source, sourceSide, sourceSlot, limit)
+  def transferBetweenInventoriesSlots(source: IInventory, sourceSide: ForgeDirection, sourceSlot: Int, sink: IInventory, sinkSide: Option[ForgeDirection], sinkSlot: Option[Int], limit: Int = 64) =
+    sinkSlot match {
+      case Some(explicitSinkSlot) =>
+        extractFromInventorySlot(
+          insertIntoInventorySlot(_, sink, sinkSide, explicitSinkSlot, limit), source, sourceSide, sourceSlot, limit)
+      case _ =>
+        extractFromInventorySlot(
+          insertIntoInventory(_, sink, sinkSide, limit), source, sourceSide, sourceSlot, limit)
+    }
 
   /**
    * Utility method for calling <tt>transferBetweenInventories</tt> on inventories
@@ -266,7 +272,7 @@ object InventoryUtils {
    * Utility method for calling <tt>transferBetweenInventoriesSlots</tt> on inventories
    * in the world.
    */
-  def transferBetweenInventoriesSlotsAt(sourcePos: BlockPosition, sourceSide: ForgeDirection, sourceSlot: Int, sinkPos: BlockPosition, sinkSide: Option[ForgeDirection], sinkSlot: Int, limit: Int = 64) =
+  def transferBetweenInventoriesSlotsAt(sourcePos: BlockPosition, sourceSide: ForgeDirection, sourceSlot: Int, sinkPos: BlockPosition, sinkSide: Option[ForgeDirection], sinkSlot: Option[Int], limit: Int = 64) =
     inventoryAt(sourcePos).exists(sourceInventory =>
       inventoryAt(sinkPos).exists(sinkInventory =>
         transferBetweenInventoriesSlots(sourceInventory, sourceSide, sourceSlot, sinkInventory, sinkSide, sinkSlot, limit)))