diff --git a/lib/fluent/env_utils.rb b/lib/fluent/env_utils.rb
index bd605db4c5..6c8abcee89 100644
--- a/lib/fluent/env_utils.rb
+++ b/lib/fluent/env_utils.rb
@@ -16,12 +16,12 @@ class OjOptions
   
       OJ_OPTIONS_ALLOWED_VALUES = {
         'bigdecimal_load': %i[bigdecimal float auto],
-        'mode': %i[strict null concat json rails object custom]
+        'mode': %i[strict null compat json rails object custom]
       }
   
       OJ_OPTIONS_DEFAULTS = {
         'bigdecimal_load': :float,
-        'mode': :concat,
+        'mode': :compat,
         'use_to_json': true
       }