diff --git a/common/buildcraft/core/inventory/TransactorSimple.java b/common/buildcraft/core/inventory/TransactorSimple.java
index d077b8da..13f23974 100644
--- a/common/buildcraft/core/inventory/TransactorSimple.java
+++ b/common/buildcraft/core/inventory/TransactorSimple.java
@@ -63,12 +63,12 @@ public class TransactorSimple extends Transactor {
 	}
 
 	protected int getEmptySlot(ItemStack stack, ForgeDirection orientation, int slotIndex) {
-		return getEmptySlot(0, inventory.getSizeInventory());
+		return getEmptySlot(stack, 0, inventory.getSizeInventory());
 	}
 
-	protected int getEmptySlot(int startSlot, int endSlot) {
+	protected int getEmptySlot(ItemStack stack, int startSlot, int endSlot) {
 		for (int i = startSlot; i < endSlot; i++)
-			if (inventory.getStackInSlot(i) == null)
+			if (inventory.getStackInSlot(i) == null && inventory.isStackValidForSlot(i, stack))
 				return i;
 
 		return -1;
diff --git a/common/buildcraft/core/inventory/TransactorVanillaSided.java b/common/buildcraft/core/inventory/TransactorVanillaSided.java
index faa862ef..c586b6c0 100644
--- a/common/buildcraft/core/inventory/TransactorVanillaSided.java
+++ b/common/buildcraft/core/inventory/TransactorVanillaSided.java
@@ -32,7 +32,7 @@ public class TransactorVanillaSided extends TransactorSimple {
         if (slotIndex >= sideSlots.length)
             return -1;
         int targetSlot = sideSlots[slotIndex];
-        return sided.canInsertItem(targetSlot, stack, orientation.ordinal()) ? targetSlot : -1;
+        return sided.isStackValidForSlot(targetSlot, stack) && sided.canInsertItem(targetSlot, stack, orientation.ordinal()) ? targetSlot : -1;
     }
 
 }