diff --git a/app/models/signature.rb b/app/models/signature.rb
index 47408858a..06ade968c 100644
--- a/app/models/signature.rb
+++ b/app/models/signature.rb
@@ -10,6 +10,8 @@ class Signature < ActiveRecord::Base
 
   delegate :signable, to: :signature_sheet
 
+  before_validation :clean_document_number
+
   def verified?
     user_exists? || in_census?
   end
@@ -58,6 +60,11 @@ class Signature < ActiveRecord::Base
     User.create!(user_params)
   end
 
+  def clean_document_number
+    return if self.document_number.blank?
+    self.document_number = self.document_number.gsub(/[^a-z0-9]+/i, "").upcase
+  end
+
   def random_password
     (0...20).map { ('a'..'z').to_a[rand(26)] }.join
   end
diff --git a/spec/models/signature_spec.rb b/spec/models/signature_spec.rb
index 6f7237484..8bb090614 100644
--- a/spec/models/signature_spec.rb
+++ b/spec/models/signature_spec.rb
@@ -13,6 +13,12 @@ describe Signature do
     it "should not be valid without a document number" do
       signature.document_number = nil
       expect(signature).to_not be_valid
+
+      signature.document_number = ""
+      expect(signature).to_not be_valid
+
+      signature.document_number = " "
+      expect(signature).to_not be_valid
     end
 
     it "should not be valid without an associated signature sheet" do
@@ -22,6 +28,24 @@ describe Signature do
 
   end
 
+  describe "#clean_document_number" do
+    it "removes non alphanumeric characters" do
+      signature = create(:signature, document_number: "123-[;,9]")
+      expect(signature.document_number).to eq("1239")
+    end
+
+    it "upcases letter in document number" do
+      signature = create(:signature, document_number: "123a")
+      expect(signature.document_number).to eq("123A")
+    end
+
+    it "deals gracefully with empty document numbers" do
+      signature = build(:signature, document_number: "")
+      signature.clean_document_number
+      expect(signature.document_number).to eq("")
+    end
+  end
+
   describe "#verified?" do
 
     it "returns true if user exists" do