diff --git a/logstash_async/formatter.py b/logstash_async/formatter.py
index cc9cf09..3f254b0 100644
--- a/logstash_async/formatter.py
+++ b/logstash_async/formatter.py
@@ -27,7 +27,6 @@ class LogstashFormatter(logging.Formatter):
 
     _basic_data_types = (type(None), bool, str, int, float)
 
-    field_skip_set = set(constants.FORMATTER_RECORD_FIELD_SKIP_LIST)
     top_level_field_set = set(constants.FORMATTER_LOGSTASH_MESSAGE_FIELD_LIST)
 
     class MessageSchema:
@@ -89,6 +88,8 @@ def __init__(
         self._prefetch_logsource()
         self._prefetch_program_name()
 
+        self.field_skip_set = set(constants.FORMATTER_RECORD_FIELD_SKIP_LIST)
+
     # ----------------------------------------------------------------------
     def _prefetch_interpreter(self):
         """Override when needed"""