diff --git a/ros2caret/verb/summary.py b/ros2caret/verb/summary.py
index ee51ae6..2549f89 100644
--- a/ros2caret/verb/summary.py
+++ b/ros2caret/verb/summary.py
@@ -44,7 +44,7 @@ def __init__(
         filters = self._get_filters(args.d_filter_args,
                                     args.s_filter_args)
         self._lttng = Lttng(args.trace_dir, event_filters=filters,
-                            validate=isinstance(args.trace_dir, list))
+                            validate=len(args.trace_dir) == 1)
         self._summary_df = self._get_summary_df(self._lttng, groupby)
         self._filtered = len(filters) > 0