diff --git a/builtin/update-index.c b/builtin/update-index.c
index ba54e19cd5..ebea285e1b 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -637,6 +637,9 @@ static int parse_new_style_cacheinfo(const char *arg,
 	unsigned long ul;
 	char *endp;
 
+	if (!arg)
+		return -1;
+
 	errno = 0;
 	ul = strtoul(arg, &endp, 8);
 	if (errno || endp == arg || *endp != ',' || (unsigned int) ul != ul)
diff --git a/t/t2107-update-index-basic.sh b/t/t2107-update-index-basic.sh
index fe2fb17102..1bafb9098c 100755
--- a/t/t2107-update-index-basic.sh
+++ b/t/t2107-update-index-basic.sh
@@ -29,6 +29,10 @@ test_expect_success 'update-index -h with corrupt index' '
 	test_i18ngrep "[Uu]sage: git update-index" broken/usage
 '
 
+test_expect_success '--cacheinfo complains of missing arguments' '
+	test_must_fail git update-index --cacheinfo
+'
+
 test_expect_success '--cacheinfo does not accept blob null sha1' '
 	echo content >file &&
 	git add file &&