diff --git a/lark/tools/nearley.py b/lark/tools/nearley.py
index 0237fcd..af2789e 100644
--- a/lark/tools/nearley.py
+++ b/lark/tools/nearley.py
@@ -186,7 +186,7 @@ def get_arg_parser():
     parser = argparse.ArgumentParser('Reads Nearley grammar (with js functions) outputs an equivalent lark parser.')
     parser.add_argument('nearley_grammar', help='Path to the file containing the nearley grammar')
     parser.add_argument('start_rule', help='Rule within the nearley grammar to make the base rule')
-    parser.add_argument('nearley_lib', help='')
+    parser.add_argument('nearley_lib', help='Path to root directory of nearley codebase (used for including builtins)')
     parser.add_argument('--es6', help='Enable experimental ES6 support', action='store_true')
     return parser