diff --git a/builtin/backfill.c b/builtin/backfill.c
index b98b0b591f..2c5ce56fb7 100644
--- a/builtin/backfill.c
+++ b/builtin/backfill.c
@@ -142,6 +142,9 @@ int cmd_backfill(int argc, const char **argv, const char *prefix, struct reposit
 	repo_init_revisions(repo, &ctx.revs, prefix);
 	argc = setup_revisions(argc, argv, &ctx.revs, NULL);
 
+	if (argc > 1)
+		die(_("unrecognized argument: %s"), argv[1]);
+
 	repo_config(repo, git_default_config, NULL);
 
 	if (ctx.sparse < 0)
diff --git a/t/t5620-backfill.sh b/t/t5620-backfill.sh
index c6f54ee91c..2c347a91fe 100755
--- a/t/t5620-backfill.sh
+++ b/t/t5620-backfill.sh
@@ -7,6 +7,14 @@ export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 
 . ./test-lib.sh
 
+test_expect_success 'backfill rejects unexpected arguments' '
+	test_must_fail git backfill unexpected-arg 2>err &&
+	test_grep "ambiguous argument .*unexpected-arg" err &&
+
+	test_must_fail git backfill --all --unexpected-arg --first-parent 2>err &&
+	test_grep "unrecognized argument: --unexpected-arg" err
+'
+
 # We create objects in the 'src' repo.
 test_expect_success 'setup repo for object creation' '
 	echo "{print \$1}" >print_1.awk &&