diff --git a/core/app/models/spree/fulfilment_changer.rb b/core/app/models/spree/fulfilment_changer.rb
index 61a4234716..1178c08f8e 100644
--- a/core/app/models/spree/fulfilment_changer.rb
+++ b/core/app/models/spree/fulfilment_changer.rb
@@ -86,9 +86,9 @@ def run!
     # we can take from the desired location, we could end up with some items being backordered.
     def run_tracking_inventory
       # Retrieve how many on hand items we can take from desired stock location
-      available_quantity = [desired_shipment.stock_location.count_on_hand(variant), default_on_hand_quantity].max
-
+      available_quantity = get_available_quantity
       new_on_hand_quantity = [available_quantity, quantity].min
+      backordered_quantity = get_backordered_quantity(available_quantity, new_on_hand_quantity)
       unstock_quantity = desired_shipment.stock_location.backorderable?(variant) ? quantity : new_on_hand_quantity
 
       ActiveRecord::Base.transaction do
@@ -105,19 +105,21 @@ def run_tracking_inventory
         # These two statements are the heart of this class. We change the number
         # of inventory units requested from one shipment to the other.
         # We order by state, because `'backordered' < 'on_hand'`.
+        # We start to move the new actual backordered quantity, so the remaining
+        # quantity can be set to on_hand state.
         current_shipment.
           inventory_units.
           where(variant: variant).
           order(state: :asc).
-          limit(new_on_hand_quantity).
-          update_all(shipment_id: desired_shipment.id, state: :on_hand)
+          limit(backordered_quantity).
+          update_all(shipment_id: desired_shipment.id, state: :backordered)
 
         current_shipment.
           inventory_units.
           where(variant: variant).
           order(state: :asc).
-          limit(quantity - new_on_hand_quantity).
-          update_all(shipment_id: desired_shipment.id, state: :backordered)
+          limit(quantity - backordered_quantity).
+          update_all(shipment_id: desired_shipment.id, state: :on_hand)
       end
     end
 
@@ -141,11 +143,22 @@ def handle_stock_counts?
       current_shipment.order.completed? && current_stock_location != desired_stock_location
     end
 
-    def default_on_hand_quantity
+    def get_available_quantity
+      if current_stock_location != desired_stock_location
+        desired_location_quantifier.positive_stock
+      else
+        sl_availability = current_location_quantifier.positive_stock
+        shipment_availability = current_shipment.inventory_units.where(variant: variant).on_hand.count
+        sl_availability + shipment_availability
+      end
+    end
+
+    def get_backordered_quantity(available_quantity, new_on_hand_quantity)
       if current_stock_location != desired_stock_location
-        0
+        quantity - new_on_hand_quantity
       else
-        current_shipment.inventory_units.where(variant: variant).on_hand.count
+        shipment_quantity = current_shipment.inventory_units.where(variant: variant).size
+        shipment_quantity - available_quantity
       end
     end
 
@@ -156,11 +169,19 @@ def current_shipment_not_already_shipped
     end
 
     def enough_stock_at_desired_location
-      unless Spree::Stock::Quantifier.new(variant, desired_stock_location).can_supply?(quantity)
+      unless desired_location_quantifier.can_supply?(quantity)
         errors.add(:desired_shipment, :not_enough_stock_at_desired_location)
       end
     end
 
+    def desired_location_quantifier
+      @desired_location_quantifier ||= Spree::Stock::Quantifier.new(variant, desired_stock_location)
+    end
+
+    def current_location_quantifier
+      @current_location_quantifier ||= Spree::Stock::Quantifier.new(variant, current_stock_location)
+    end
+
     def desired_shipment_different_from_current
       if desired_shipment.id == current_shipment.id
         errors.add(:desired_shipment, :can_not_transfer_within_same_shipment)