diff --git a/src/csfilter-kfp b/src/csfilter-kfp
index 2a94888..bf3169a 100755
--- a/src/csfilter-kfp
+++ b/src/csfilter-kfp
@@ -198,7 +198,7 @@ def main():
         help="file to store all excluded findings to")
 
     parser.add_argument(
-        "--json-output", action="store_true", default=(not os.isatty(sys.stdout.fileno())),
+        "--json-output", action="store_true", default=(not sys.stdout.isatty()),
         help="produce JSON output (default if stdout is not connected to a terminal)")
 
     parser.add_argument(