diff --git a/app/models/enterprise_relationship.rb b/app/models/enterprise_relationship.rb
index 49c26cb0f8..de06a0578e 100644
--- a/app/models/enterprise_relationship.rb
+++ b/app/models/enterprise_relationship.rb
@@ -33,8 +33,8 @@ class EnterpriseRelationship < ActiveRecord::Base
     relatives = {}
 
     relationships.each do |r|
-      relatives[r.parent_id] ||= {distributors: [], producers: []}
-      relatives[r.child_id]  ||= {distributors: [], producers: []}
+      relatives[r.parent_id] ||= {distributors: Set.new, producers: Set.new}
+      relatives[r.child_id]  ||= {distributors: Set.new, producers: Set.new}
 
       if !activated_only || r.child.activated?
         relatives[r.parent_id][:producers]    << r.child_id if r.child.is_primary_producer
diff --git a/spec/models/enterprise_relationship_spec.rb b/spec/models/enterprise_relationship_spec.rb
index 59e36c37e5..96f80a65a4 100644
--- a/spec/models/enterprise_relationship_spec.rb
+++ b/spec/models/enterprise_relationship_spec.rb
@@ -74,21 +74,27 @@ describe EnterpriseRelationship do
     let(:e1) { create(:supplier_enterprise) }
     let(:e2) { create(:supplier_enterprise, sells: 'any') }
     let!(:er) { create(:enterprise_relationship, parent: e1, child: e2) }
+    let(:er_reverse) { create(:enterprise_relationship, parent: e2, child: e1) }
 
     it "categorises enterprises into distributors and producers" do
       EnterpriseRelationship.relatives.should ==
-        {e1.id => {distributors: [e2.id], producers: [e2.id]},
-         e2.id => {distributors: [],      producers: [e1.id]}}
+        {e1.id => {distributors: Set.new([e2.id]), producers: Set.new([e2.id])},
+         e2.id => {distributors: Set.new([]),      producers: Set.new([e1.id])}}
     end
 
     it "finds inactive enterprises by default" do
       e1.update_attribute :confirmed_at, nil
-      EnterpriseRelationship.relatives[e2.id][:producers].should == [e1.id]
+      EnterpriseRelationship.relatives[e2.id][:producers].should == Set.new([e1.id])
     end
 
     it "does not find inactive enterprises when requested" do
       e1.update_attribute :confirmed_at, nil
       EnterpriseRelationship.relatives(true)[e2.id][:producers].should be_empty
     end
+
+    it "does not show duplicates" do
+      er_reverse
+      EnterpriseRelationship.relatives[e2.id][:producers].should == Set.new([e1.id])
+    end
   end
 end