diff --git a/h5p-development.class.php b/h5p-development.class.php
index 75e9daf..7f33689 100644
--- a/h5p-development.class.php
+++ b/h5p-development.class.php
@@ -93,6 +93,7 @@ class H5PDevelopment {
     // TODO: Should we remove libraries without files? Not really needed, but must be cleaned up some time, right?
 
     // Go trough libraries and insert dependencies. Missing deps. will just be ignored and not available. (I guess?!)
+    $this->h5pF->lockDependencyStorage();
     foreach ($this->libraries as $library) {
       $this->h5pF->deleteLibraryDependencies($library['libraryId']);
       // This isn't optimal, but without it we would get duplicate warnings.
@@ -104,6 +105,7 @@ class H5PDevelopment {
         }
       }
     }
+    $this->h5pF->unlockDependencyStorage();
     // TODO: Deps must be inserted into h5p_nodes_libraries as well... ? But only if they are used?!
   }
 
diff --git a/h5p.classes.php b/h5p.classes.php
index 0830735..0164f1f 100644
--- a/h5p.classes.php
+++ b/h5p.classes.php
@@ -408,6 +408,17 @@ interface H5PFrameworkInterface {
    */
   public function deleteLibraryDependencies($libraryId);
 
+  /**
+   * Start an atomic operation against the dependency storage
+   */
+  public function lockDependencyStorage();
+  
+  /**
+   * Stops an atomic operation against the dependency storage
+   */
+  public function unlockDependencyStorage();
+  
+  
   /**
    * Delete a library from database and file system
    *
@@ -1433,7 +1444,7 @@ Class H5PExport {
       'title' => $content['title'],
       // TODO - stop using 'und', this is not the preferred way.
       // Either remove language from the json if not existing, or use "language": null
-      'language' => isset($content['language']) ? $content['language'] : 'und',
+      'language' => (isset($content['language']) && strlen(trim($content['language'])) !== 0) ? $content['language'] : 'und',
       'mainLibrary' => $content['library']['name'],
       'embedTypes' => $embedTypes,
     );
@@ -1465,7 +1476,7 @@ Class H5PExport {
 
     // Create new zip instance.
     $zip = new ZipArchive();
-    $zip->open($zipPath, ZIPARCHIVE::CREATE);
+    $zip->open($zipPath, ZIPARCHIVE::CREATE | ZIPARCHIVE::OVERWRITE);
 
     // Get all files and folders in $tempPath
     $iterator = new RecursiveIteratorIterator(new RecursiveDirectoryIterator($tempPath . DIRECTORY_SEPARATOR));