diff --git a/README.markdown b/README.markdown
index 6937e4fc..235f7a2b 100644
--- a/README.markdown
+++ b/README.markdown
@@ -29,7 +29,7 @@ check out one of the versioned branches.
 # Requirements
 
 - MySQL/MariaDB 5.1+ (with experimental support for PostgreSQL 9+ and SQLite 3)
-- [Stable PHP](https://en.wikipedia.org/wiki/PHP#Release_history) (7.0+ as of writing)
+- [Stable PHP](https://en.wikipedia.org/wiki/PHP#Release_history) (7.1+ as of writing)
 - GD or ImageMagick
 
 # Installation
diff --git a/core/_install.php b/core/_install.php
index 3a876a7d..177a1267 100644
--- a/core/_install.php
+++ b/core/_install.php
@@ -120,6 +120,7 @@ function do_install() { // {{{
 		return;
 	}
 
+	define("CACHE_DSN", null);
 	define("DEBUG_SQL", false);
 	define("DATABASE_KA", true);
 	install_process();
diff --git a/core/cacheengine.php b/core/cacheengine.php
index e1b0b71d..40be954e 100644
--- a/core/cacheengine.php
+++ b/core/cacheengine.php
@@ -138,7 +138,7 @@ class Cache {
 	public $hits=0, $misses=0;
 	public $time=0;
 
-	public function __construct($dsn: string) {
+	public function __construct(?string $dsn) {
 		$matches = array();
 		if($dsn && preg_match("#(.*)://(.*)#", $dsn, $matches)) {
 			if($matches[1] == "memcache") {
@@ -177,7 +177,7 @@ class Cache {
 	}
 
 	public function set(string $key, $val, int $time=0) {
-		$this->engine->set($key, $time, $val);
+		$this->engine->set($key, $val, $time);
 		if((DEBUG_CACHE === true) || (is_null(DEBUG_CACHE) && @$_GET['DEBUG_CACHE'])) {
 			file_put_contents("data/cache.log", "Cache set: $key ($time)\n", FILE_APPEND);
 		}
diff --git a/core/database.php b/core/database.php
index 53deef35..c33db38e 100644
--- a/core/database.php
+++ b/core/database.php
@@ -45,7 +45,7 @@ class Database {
 	 * DB connection is on-demand.
 	 */
 	public function __construct() {
-		$this->cache = Cache(CACHE_DSN);
+		$this->cache = new Cache(CACHE_DSN);
 	}
 
 	private function connect_db() {