diff --git a/lib/logstash/plugin_mixins/ecs_compatibility_support.rb b/lib/logstash/plugin_mixins/ecs_compatibility_support.rb
index b18729d..a59dcbe 100644
--- a/lib/logstash/plugin_mixins/ecs_compatibility_support.rb
+++ b/lib/logstash/plugin_mixins/ecs_compatibility_support.rb
@@ -48,7 +48,7 @@ def self.extended(base)
       module LegacyAdapter
         def self.included(base)
           base.extend(ArgumentValidator)
-          base.config(:ecs_compatibility, :validate => :ecs_compatibility_argument, :default => :disabled)
+          base.config(:ecs_compatibility, :validate => :ecs_compatibility_argument, :default => 'disabled')
         end
 
         ##