diff --git a/btrfsck.c b/btrfsck.c
index 4bfa55c5..a3f803e9 100644
--- a/btrfsck.c
+++ b/btrfsck.c
@@ -709,6 +709,11 @@ int check_extent_refs(struct btrfs_root *root,
 	return err;
 }
 
+void print_usage(void) {
+	fprintf(stderr, "usage: btrfsck dev\n");
+	exit(1);
+}
+
 int main(int ac, char **av) {
 	struct btrfs_root *root;
 	struct cache_tree extent_cache;
@@ -727,6 +732,9 @@ int main(int ac, char **av) {
 	int slot;
 	struct btrfs_root_item ri;
 
+	if (ac < 2)
+		print_usage();
+
 	radix_tree_init();
 	cache_tree_init(&extent_cache);
 	cache_tree_init(&seen);