diff --git a/app/models/spree/variant.rb b/app/models/spree/variant.rb
index 2937687af7..d4f3c3aade 100644
--- a/app/models/spree/variant.rb
+++ b/app/models/spree/variant.rb
@@ -59,6 +59,8 @@ module Spree
       %w(weight volume).include?(variant.product.andand.variant_unit)
     }
 
+    validates :unit_value, numericality: { greater_than: 0 }
+
     validates :unit_description, presence: true, if: ->(variant) {
       variant.product.andand.variant_unit.present? && variant.unit_value.nil?
     }
diff --git a/db/migrate/20210414171109_add_unit_value_constraint.rb b/db/migrate/20210414171109_add_unit_value_constraint.rb
new file mode 100644
index 0000000000..ac34a8d15a
--- /dev/null
+++ b/db/migrate/20210414171109_add_unit_value_constraint.rb
@@ -0,0 +1,10 @@
+class AddUnitValueConstraint < ActiveRecord::Migration[5.0]
+  def up
+    execute "UPDATE spree_variants SET unit_value = 1 WHERE unit_value <= 0"
+    execute "ALTER TABLE spree_variants ADD CONSTRAINT positive_unit_value CHECK (unit_value > 0)"
+  end
+
+  def down
+    execute "ALTER TABLE spree_variants DROP CONSTRAINT positive_unit_value"
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 310cc0420f..db58a7a083 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20210326094519) do
+ActiveRecord::Schema.define(version: 20210414171109) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
diff --git a/spec/controllers/api/v0/variants_controller_spec.rb b/spec/controllers/api/v0/variants_controller_spec.rb
index a7b3d70b81..439a03e22d 100644
--- a/spec/controllers/api/v0/variants_controller_spec.rb
+++ b/spec/controllers/api/v0/variants_controller_spec.rb
@@ -130,7 +130,7 @@ describe Api::V0::VariantsController, type: :controller do
 
     it "can create a new variant" do
       original_number_of_variants = variant.product.variants.count
-      api_post :create, variant: { sku: "12345", unit_value: "weight", unit_description: "L" }, product_id: variant.product.to_param
+      api_post :create, variant: { sku: "12345", unit_value: "1", unit_description: "L" }, product_id: variant.product.to_param
 
       expect(attributes.all?{ |attr| json_response.include? attr.to_s }).to eq(true)
       expect(response.status).to eq(201)
diff --git a/spec/models/spree/variant_spec.rb b/spec/models/spree/variant_spec.rb
index 239962a655..3589df55aa 100644
--- a/spec/models/spree/variant_spec.rb
+++ b/spec/models/spree/variant_spec.rb
@@ -18,6 +18,11 @@ module Spree
         variant.price = 0
         expect(variant).to be_valid
       end
+
+      it "should validate unit_value is greater than 0" do
+        variant.unit_value = 0
+        expect(variant).to be_invalid
+      end
     end
 
     context "price parsing" do