diff --git a/src/DatasetManager.php b/src/DatasetManager.php
index c13a591..ec461ce 100644
--- a/src/DatasetManager.php
+++ b/src/DatasetManager.php
@@ -84,7 +84,7 @@ class DatasetManager
         if (file_exists($fn)) {
             $versions = include $fn;
             foreach ($versions['versions'] as $name=>$version) {
-                self::$packageVersions[$name] = $version['version'];
+                self::$packageVersions[$name] = array_key_exists('version',$version) ? $version['version'] : null;
             }
         }