diff --git a/locust/argument_parser.py b/locust/argument_parser.py
index 09cac036b2..3747ca7034 100644
--- a/locust/argument_parser.py
+++ b/locust/argument_parser.py
@@ -559,7 +559,7 @@ def setup_parser_arguments(parser):
         "--legacy-ui",
         default=False,
         action="store_true",
-        help="Use the legacy frontend for the web UI",
+        help="Use the legacy frontend for the web UI (deprecated, support will be removed soon)",
         env_var="LOCUST_LEGACY_UI",
     )
 
diff --git a/locust/main.py b/locust/main.py
index 2ee09f3884..849aeda1a2 100644
--- a/locust/main.py
+++ b/locust/main.py
@@ -182,6 +182,9 @@ def is_valid_percentile(parameter):
         sys.stderr.write("[DEPRECATED] The --hatch-rate parameter has been renamed --spawn-rate\n")
         options.spawn_rate = options.hatch_rate
 
+    if options.legacy_ui:
+        sys.stderr.write("[DEPRECATED] The legacy UI is deprecated and will be removed soon\n")
+
     # setup logging
     if not options.skip_log_setup:
         if options.loglevel.upper() in ["DEBUG", "INFO", "WARNING", "ERROR", "CRITICAL"]: