diff --git a/app/models/spree/product_distribution.rb b/app/models/spree/product_distribution.rb
index 2a73d464ca..cacdf496f0 100644
--- a/app/models/spree/product_distribution.rb
+++ b/app/models/spree/product_distribution.rb
@@ -5,5 +5,7 @@ module Spree
     belongs_to :product
     belongs_to :distributor
     belongs_to :shipping_method
+
+    validates_uniqueness_of :product_id, :scope => :distributor_id
   end
 end
diff --git a/spec/models/product_distribution_spec.rb b/spec/models/product_distribution_spec.rb
new file mode 100644
index 0000000000..7827b32a8a
--- /dev/null
+++ b/spec/models/product_distribution_spec.rb
@@ -0,0 +1,23 @@
+require 'spec_helper'
+
+describe Spree::ProductDistribution do
+  it "is unique for scope [product, distributor]" do
+    pd1 = create(:product_distribution)
+    pd1.should be_valid
+
+    new_product = create(:product)
+    new_distributor = create(:distributor)
+
+    pd2 = build(:product_distribution, :product => pd1.product, :distributor => pd1.distributor)
+    pd2.should_not be_valid
+
+    pd2 = build(:product_distribution, :product => pd1.product, :distributor => new_distributor)
+    pd2.should be_valid
+
+    pd2 = build(:product_distribution, :product => new_product, :distributor => pd1.distributor)
+    pd2.should be_valid
+
+    pd2 = build(:product_distribution, :product => new_product, :distributor => new_distributor)
+    pd2.should be_valid
+  end
+end