diff --git a/app/models/spree/variant.rb b/app/models/spree/variant.rb
index 9b8fe730ca..d8782c9936 100644
--- a/app/models/spree/variant.rb
+++ b/app/models/spree/variant.rb
@@ -65,6 +65,7 @@ module Spree
 
     before_validation :set_cost_currency
     before_validation :update_weight_from_unit_value, if: ->(v) { v.product.present? }
+    before_validation :ensure_unit_value
 
     after_save :save_default_price
     after_save :update_units
@@ -297,5 +298,11 @@ module Spree
       exchange_variants(:reload).destroy_all
       yield
     end
+
+    def ensure_unit_value
+      return unless product&.variant_unit == "items" && unit_value.nil?
+
+      self.unit_value = 1.0
+    end
   end
 end
diff --git a/spec/models/spree/variant_spec.rb b/spec/models/spree/variant_spec.rb
index 333b039f39..530d8be080 100644
--- a/spec/models/spree/variant_spec.rb
+++ b/spec/models/spree/variant_spec.rb
@@ -783,4 +783,17 @@ module Spree
       expect(e.reload.variant_ids).to be_empty
     end
   end
+
+  describe "#ensure_unit_value" do
+    let(:product) { create(:product, variant_unit: "weight") }
+    let(:variant) { create(:variant, product_id: product.id) }
+
+    context "when a product's variant_unit value is changed from weight to items" do
+      it "sets the variant's unit_value to 1" do
+        product.update(variant_unit: "items")
+
+        expect(variant.unit_value).to eq 1
+      end
+    end
+  end
 end