usage(builtin_diff_usage);
                argv++; argc--;
        }
-       if (!cached)
-               setup_work_tree();
        /*
         * Make sure there is one revision (i.e. pending object),
         * and there is no revision filtering parameters.
            revs->max_count != -1 || revs->min_age != -1 ||
            revs->max_age != -1)
                usage(builtin_diff_usage);
-       if (read_cache_preload(revs->diffopt.pathspec.raw) < 0) {
-               perror("read_cache_preload");
+       if (!cached) {
+               setup_work_tree();
+               if (read_cache_preload(revs->diffopt.pathspec.raw) < 0) {
+                       perror("read_cache_preload");
+                       return -1;
+               }
+       } else if (read_cache() < 0) {
+               perror("read_cache");
                return -1;
        }
        return run_diff_index(revs, cached);