diff --git a/src/App/Service/GalleryService.php b/src/App/Service/GalleryService.php
index 28b14ed..2dc5f8e 100644
--- a/src/App/Service/GalleryService.php
+++ b/src/App/Service/GalleryService.php
@@ -52,10 +52,16 @@ class GalleryService
     if(file_exists($exportName)) {
       return $exportName;
     }
+    $exportLock = sprintf("data/tmp/%s.lock", $dir);
+
+    if(file_exists($exportLock)) {
+      return false;
+    }
 
     $images = array_map('basename', glob($this->getImageDir($dir) . "*.{jpg,jpeg,png}", GLOB_BRACE));
 
     $zipName = tempnam("data/tmp", "export");
+    touch($exportLock);
     $zipArchive = new \ZipArchive();
     $zipArchive->open($zipName, \ZipArchive::CREATE);
     foreach ($images as $image) {
@@ -67,6 +73,7 @@ class GalleryService
     }
     $zipArchive->close();
     rename($zipName, $exportName);
+    unlink($exportLock);
     return $exportName;
   }