diff --git a/lib/active_model_serializers/adapter/json_api/deserialization.rb b/lib/active_model_serializers/adapter/json_api/deserialization.rb
index 2e0e531dd..500dae79d 100644
--- a/lib/active_model_serializers/adapter/json_api/deserialization.rb
+++ b/lib/active_model_serializers/adapter/json_api/deserialization.rb
@@ -141,6 +141,7 @@ def validate_payload(payload)
 
         # @api private
         def filter_fields(fields, options)
+          KeyTransform.send(:underscore, fields)
           if (only = options[:only])
             fields.slice!(*Array(only).map(&:to_s))
           elsif (except = options[:except])