diff --git a/dvc/command/diff.py b/dvc/command/diff.py
index ca5245d71..08e91dbc9 100644
--- a/dvc/command/diff.py
+++ b/dvc/command/diff.py
@@ -135,7 +135,7 @@ def add_parser(subparsers, parent_parser):
         "--target",
         default=None,
         help=(
-            "Source path to a data file or directory. Default None,"
+            "Source path to a data file or directory. Default None."
             "If not specified, compares all files and directories "
             "that are under DVC control in the current working space."
         ),