diff --git a/lib/raven/processor/sanitizedata.rb b/lib/raven/processor/sanitizedata.rb
index <HASH>..<HASH> 100644
--- a/lib/raven/processor/sanitizedata.rb
+++ b/lib/raven/processor/sanitizedata.rb
@@ -37,7 +37,7 @@ module Raven
     end
 
     def fields_re
-      @fields_re ||= /(#{(DEFAULT_FIELDS + @sanitize_fields).join("|")})/i
+      @fields_re ||= /(#{(DEFAULT_FIELDS | @sanitize_fields).join("|")})/i
     end
   end
 end
diff --git a/spec/raven/configuration_spec.rb b/spec/raven/configuration_spec.rb
index <HASH>..<HASH> 100644
--- a/spec/raven/configuration_spec.rb
+++ b/spec/raven/configuration_spec.rb
@@ -130,4 +130,16 @@ describe Raven::Configuration do
     end
   end
 
+  context 'configuration for sanitize fields' do
+    it 'should union default sanitize fields with user-defined sanitize fields' do
+      fields = Raven::Processor::SanitizeData::DEFAULT_FIELDS | %w(test monkeybutt)
+
+      subject.sanitize_fields = fields
+      client = Raven::Client.new(subject)
+      processor = Raven::Processor::SanitizeData.new(client)
+
+      expect(processor.send(:fields_re)).to eq(/(#{fields.join('|')})/i)
+    end
+  end
+
 end
union instead of concatenation, because duplicate fields