diff --git a/lib/resource_generator.rb b/lib/resource_generator.rb
index 9e702e6..173b3bd 100644
--- a/lib/resource_generator.rb
+++ b/lib/resource_generator.rb
@@ -440,7 +440,7 @@ def self.apply_invariants!(resource)
         when FHIR::CommunicationRequest
           resource.payload = nil
         when FHIR::Composition
-          resource.attester.each {|a| a.mode = ['professional']}
+          resource.attester.each {|a| a.mode = 'professional'}
           resource.section.each do |section|
             section.emptyReason = nil
             section.section.each do |sub|