bases[bases_count++] = sha;
                }
                else
-                       warning("Cannot handle more than %zu bases. "
-                               "Ignoring %s.", ARRAY_SIZE(bases)-1, argv[i]);
+                       warning("Cannot handle more than %d bases. "
+                               "Ignoring %s.",
+                               (int)ARRAY_SIZE(bases)-1, argv[i]);
        }
        if (argc - i != 3) /* "--" "<head>" "<remote>" */
                die("Not handling anything other than two heads merge.");