diff --git a/builtin-grep.c b/builtin-grep.c
index 0ef849cb84..e3eeb77cc7 100644
--- a/builtin-grep.c
+++ b/builtin-grep.c
@@ -762,8 +762,9 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
 	struct option options[] = {
 		OPT_BOOLEAN(0, "cached", &cached,
 			"search in index instead of in the work tree"),
-		OPT_BOOLEAN(0, "index", &use_index,
-			"--no-index finds in contents not managed by git"),
+		{ OPTION_BOOLEAN, 0, "index", &use_index, NULL,
+			"finds in contents not managed by git",
+			PARSE_OPT_NOARG | PARSE_OPT_NEGHELP },
 		OPT_GROUP(""),
 		OPT_BOOLEAN('v', "invert-match", &opt.invert,
 			"show non-matching lines"),