diff --git a/kopf/_core/actions/loggers.py b/kopf/_core/actions/loggers.py
index 0e40efb5..411151a4 100644
--- a/kopf/_core/actions/loggers.py
+++ b/kopf/_core/actions/loggers.py
@@ -29,7 +29,7 @@ class LogFormat(enum.Enum):
     """ Log formats, as specified on CLI. """
     PLAIN = '%(message)s'
     FULL = '[%(asctime)s] %(name)-20.20s [%(levelname)-8.8s] %(message)s'
-    JSON = enum.auto()
+    JSON = '-json-'  # not used for formatting, only for detection
 
 
 class ObjectFormatter(logging.Formatter):