diff --git a/app/models/bill_signature.rb b/app/models/bill_signature.rb
index a6f41b33a..3828c2f1f 100644
--- a/app/models/bill_signature.rb
+++ b/app/models/bill_signature.rb
@@ -49,7 +49,7 @@ class BillSignature < ApplicationRecord
   end
 
   def set_signature(signature, day)
-    signature.attach(
+    self.signature.attach(
       io: StringIO.new(signature),
       filename: "demarches-simplifiees-signature-#{day.to_date.iso8601}.der",
       content_type: 'application/x-x509-ca-cert'
diff --git a/spec/models/bill_signature_spec.rb b/spec/models/bill_signature_spec.rb
index d951dc5cd..a31c399e6 100644
--- a/spec/models/bill_signature_spec.rb
+++ b/spec/models/bill_signature_spec.rb
@@ -161,4 +161,16 @@ RSpec.describe BillSignature, type: :model do
       it { expect(bill_signature.serialized.filename).to eq('demarches-simplifiees-operations-1871-03-18.json') }
     end
   end
+
+  describe '#set_signature' do
+    let(:bill_signature) { BillSignature.new }
+    let(:signature) { 'une belle signature' }
+    let(:day) { Time.zone.parse('12/12/2012') }
+
+    before { bill_signature.set_signature(signature, day) }
+
+    it { expect(bill_signature.signature.attached?).to be(true) }
+    it { expect(bill_signature.signature.filename.to_s).to eq('demarches-simplifiees-signature-2012-12-12.der') }
+    it { expect(bill_signature.signature.content_type).to eq('application/x-x509-ca-cert') }
+  end
 end