diff --git a/includes/Wpup/FileCache.php b/includes/Wpup/FileCache.php
index fa2dda1..3a165a5 100644
--- a/includes/Wpup/FileCache.php
+++ b/includes/Wpup/FileCache.php
@@ -1,6 +1,14 @@
 <?php
 /**
  * A simple file-based cache.
+ *
+ * @internal Data is base64 encoded to avoid unserialization issues ('unserialize(): Error at offset') which
+ * could be caused by:
+ * - inconsistent line endings
+ * - unescaped quotes/slashes etc
+ * - miscounted unicode characters
+ *
+ * @see https://github.com/YahnisElsts/wp-update-server/pull/11
  */
 class Wpup_FileCache implements Wpup_Cache {
 	protected $cacheDirectory;
@@ -18,7 +26,7 @@ public function __construct($cacheDirectory) {
 	public function get($key) {
 		$filename = $this->getCacheFilename($key);
 		if ( is_file($filename) && is_readable($filename) ) {
-			$cache = unserialize(file_get_contents($filename));
+			$cache = unserialize(base64_decode(file_get_contents($filename)));
 			if ( $cache['expiration_time'] < time() ) {
 				return null; //Cache expired.
 			} else {
@@ -41,7 +49,7 @@ public function set($key, $value, $expiration = 0) {
 			'expiration_time' => time() + $expiration,
 			'value' => $value,
 		);
-		file_put_contents($this->getCacheFilename($key), serialize($cache));
+		file_put_contents($this->getCacheFilename($key), base64_encode(serialize($cache)));
 	}
 
 	/**
diff --git a/includes/Wpup/Package.php b/includes/Wpup/Package.php
index 24ad4f1..4b97c84 100644
--- a/includes/Wpup/Package.php
+++ b/includes/Wpup/Package.php
@@ -75,7 +75,7 @@ public function getMetadata() {
 	 */
 	public static function fromArchive($filename, $slug = null, Wpup_Cache $cache = null) {
 		$modified = filemtime($filename);
-		$cacheKey = 'metadata-' . md5($filename . '|' . filesize($filename) . '|' . $modified);
+		$cacheKey = 'metadata-b64-' . $slug . '-' . md5($filename . '|' . filesize($filename) . '|' . $modified);
 		$metadata = null;
 
 		//Try the cache first.