diff --git a/app/models/spree/line_item_decorator.rb b/app/models/spree/line_item_decorator.rb
index 7bc718e857..58ca4c2b39 100644
--- a/app/models/spree/line_item_decorator.rb
+++ b/app/models/spree/line_item_decorator.rb
@@ -8,7 +8,7 @@ Spree::LineItem.class_eval do
   # Redefining here to add the inverse_of option
   belongs_to :order, :class_name => "Spree::Order", inverse_of: :line_items
 
-  # Allows manual skipping of stock_availability check
+  # Allows manual skipping of Stock::AvailabilityValidator
   attr_accessor :skip_stock_check
 
   attr_accessible :max_quantity, :final_weight_volume, :price
@@ -133,13 +133,6 @@ Spree::LineItem.class_eval do
   end
   alias_method_chain :update_inventory, :scoping
 
-  # Override of Spree validation method
-  # Added check for in-memory :skip_stock_check attribute
-  def stock_availability
-    return if skip_stock_check || sufficient_stock?
-    errors.add(:quantity, I18n.t('validation.exceeds_available_stock'))
-  end
-
   def scoper
     @scoper ||= OpenFoodNetwork::ScopeVariantToHub.new(order.distributor)
   end
diff --git a/app/models/spree/stock/availability_validator_decorator.rb b/app/models/spree/stock/availability_validator_decorator.rb
new file mode 100644
index 0000000000..29f9d0413c
--- /dev/null
+++ b/app/models/spree/stock/availability_validator_decorator.rb
@@ -0,0 +1,41 @@
+Spree::Stock::AvailabilityValidator.class_eval do
+  def validate(line_item)
+    # OFN specific check for in-memory :skip_stock_check attribute
+    return if line_item.skip_stock_check
+
+    quantity_to_validate = line_item.quantity - quantity_in_shipment(line_item)
+    return if quantity_to_validate < 1
+
+    validate_quantity(line_item, quantity_to_validate)
+  end
+
+  private
+
+  # This is an adapted version of a fix to the inventory_units not being considered here.
+  # See #3090 for details.
+  # This can be removed after upgrading to Spree 2.4.
+  def quantity_in_shipment(line_item)
+    shipment = line_item_shipment(line_item)
+    return 0 unless shipment
+
+    units = shipment.inventory_units_for(line_item.variant)
+    units.count
+  end
+
+  def line_item_shipment(line_item)
+    return line_item.target_shipment if line_item.target_shipment
+    return line_item.order.shipments.first if line_item.order.present? && line_item.order.shipments.any?
+  end
+
+  # This is the spree v2.0.4 implementation of validate
+  # But using the calculated quantity instead of the line_item.quantity.
+  def validate_quantity(line_item, quantity)
+    quantifier = Spree::Stock::Quantifier.new(line_item.variant_id)
+    return if quantifier.can_supply? quantity
+
+    variant = line_item.variant
+    display_name = %Q{#{variant.name}}
+    display_name += %Q{ (#{variant.options_text})} unless variant.options_text.blank?
+    line_item.errors[:quantity] << Spree.t(:out_of_stock, :scope => :order_populator, :item => display_name.inspect)
+  end
+end
diff --git a/spec/features/admin/bulk_order_management_spec.rb b/spec/features/admin/bulk_order_management_spec.rb
index e6a3423868..6cbdd615b2 100644
--- a/spec/features/admin/bulk_order_management_spec.rb
+++ b/spec/features/admin/bulk_order_management_spec.rb
@@ -139,11 +139,10 @@ feature %q{
     end
 
     context "submitting data to the server" do
-      let!(:o1) { create(:order_with_distributor, state: 'complete', completed_at: Time.zone.now ) }
-      let!(:li1) { create(:line_item_with_shipment, order: o1, :quantity => 5 ) }
+      let!(:order) { create(:completed_order_with_fees) }
 
       before :each do
-        li1.variant.update_attributes(on_hand: 1, on_demand: false)
+        order.line_items.second.destroy # we keep only one line item for this test
         visit '/admin/orders/bulk_management'
       end
 
@@ -162,13 +161,14 @@ feature %q{
       context "when unacceptable data is sent to the server" do
         it "displays an update button which submits pending changes" do
           expect(page).to have_no_selector "#save-bar"
-          fill_in "quantity", :with => li1.variant.on_hand + li1.quantity + 10
+          line_item = order.line_items.first
+          fill_in "quantity", :with => line_item.variant.on_hand + line_item.quantity + 10
           expect(page).to have_selector "input[name='quantity'].ng-dirty"
           expect(page).to have_selector "#save-bar", text: "You have unsaved changes"
           click_button "Save Changes"
           expect(page).to have_selector "#save-bar", text: "Fields with red borders contain errors."
           expect(page).to have_selector "input[name='quantity'].ng-dirty.update-error"
-          expect(page).to have_content "exceeds available stock. Please ensure line items have a valid quantity."
+          expect(page).to have_content "is out of stock"
         end
       end
     end
diff --git a/spec/models/spree/line_item_spec.rb b/spec/models/spree/line_item_spec.rb
index 4690285be3..9f85774bf9 100644
--- a/spec/models/spree/line_item_spec.rb
+++ b/spec/models/spree/line_item_spec.rb
@@ -585,24 +585,5 @@ module Spree
         }.to change(Spree::OptionValue, :count).by(0)
       end
     end
-
-    describe "checking stock availability" do
-      let(:line_item) { LineItem.new }
-
-      context "when skip_stock_check is not set" do
-        it "checks stock" do
-          expect(line_item).to receive(:sufficient_stock?) { true }
-          line_item.send(:stock_availability)
-        end
-      end
-
-      context "when skip_stock_check is set to true" do
-        before { line_item.skip_stock_check = true }
-        it "does not check stock" do
-          expect(line_item).to_not receive(:sufficient_stock?)
-          line_item.send(:stock_availability)
-        end
-      end
-    end
   end
 end
diff --git a/spec/models/spree/stock/availability_validator_spec.rb b/spec/models/spree/stock/availability_validator_spec.rb
new file mode 100644
index 0000000000..de14a5a1c0
--- /dev/null
+++ b/spec/models/spree/stock/availability_validator_spec.rb
@@ -0,0 +1,56 @@
+require 'spec_helper'
+
+module Spree
+  module Stock
+    describe AvailabilityValidator do
+      let(:validator) { AvailabilityValidator.new({}) }
+
+      context "line item without existing inventory units" do
+        let(:order) { create(:order_with_line_items) }
+        let(:line_item) { order.line_items.first }
+
+        context "available quantity when variant.on_hand > line_item.quantity" do
+          it "suceeds" do
+            line_item.quantity = line_item.variant.on_hand - 1
+            validator.validate(line_item)
+            expect(line_item).to be_valid
+          end
+        end
+
+        context "unavailable quantity when variant.on_hand < line_item.quantity" do
+          it "fails" do
+            line_item.quantity = line_item.variant.on_hand + 1
+            validator.validate(line_item)
+            expect(line_item).not_to be_valid
+          end
+
+          it "succeeds with line_item skip_stock_check" do
+            line_item.skip_stock_check = true
+            line_item.quantity = line_item.variant.on_hand + 1
+            validator.validate(line_item)
+            expect(line_item).to be_valid
+          end
+        end
+      end
+
+      describe "line item with existing inventory units" do
+        let(:order) { create(:completed_order_with_totals) }
+        let(:line_item) { order.line_items.first }
+
+        context "when adding all variant.on_hand quantity to existing line_item quantity" do
+          it "succeeds because it excludes existing inventory units from the validation" do
+            line_item.quantity += line_item.variant.on_hand
+            validator.validate(line_item)
+            expect(line_item).to be_valid
+          end
+
+          it "fails if one more item is added" do
+            line_item.quantity += line_item.variant.on_hand + 1
+            validator.validate(line_item)
+            expect(line_item).not_to be_valid
+          end
+        end
+      end
+    end
+  end
+end