diff --git a/lib/has_attachments.rb b/lib/has_attachments.rb
index b561b8bc..8b92ec38 100644
--- a/lib/has_attachments.rb
+++ b/lib/has_attachments.rb
@@ -25,7 +25,9 @@ def has_attachments(options={})
           writeable: true,
           setter: ->(req) {
             req[:doc]['images'].each do |img|
-              self.images.attach(img['signed_id'])
+              unless self.images.detect{|i| i.signed_id == img['signed_id'] }
+                self.images.attach(img['signed_id'])
+              end
             end
           },
           getter: ->(*) {
diff --git a/spec/representers/api/v1/exercises/representer_spec.rb b/spec/representers/api/v1/exercises/representer_spec.rb
index f8617e18..9a201b31 100644
--- a/spec/representers/api/v1/exercises/representer_spec.rb
+++ b/spec/representers/api/v1/exercises/representer_spec.rb
@@ -89,8 +89,10 @@ module Api::V1::Exercises
     end
 
     context 'images' do
-      it 'are included' do
+      before(:each) do
         exercise.images.attach(io: File.open(Rails.root.join('public', 'favicon.ico')), filename: 'favicon.ico', content_type: 'image/jpeg')
+      end
+      it 'are included' do
         expect(representation).to(
           including(
             'images' => [a_hash_including(
@@ -107,6 +109,20 @@ module Api::V1::Exercises
         )
       end
 
+      it 'only attaches when not already attached' do
+        expect {
+          # attempt to attach an image that is already attached
+          representer = described_class.new(exercise)
+          expect {
+            representer.from_hash('images' => [
+                                    { 'signed_id' => exercise.images[0].signed_id },
+                                    { 'signed_id' => exercise.images[0].signed_id },
+                                  ]
+                                 )
+            exercise.save
+          }.not_to change { exercise.images.count }
+      end
+
     end
 
     context 'questions' do