diff --git a/src/ePub/Loader/ZipFileLoader.php b/src/ePub/Loader/ZipFileLoader.php
index e7c4f4d..8bf65b3 100644
--- a/src/ePub/Loader/ZipFileLoader.php
+++ b/src/ePub/Loader/ZipFileLoader.php
@@ -37,7 +37,8 @@ public function load($file)
             $ns = $package->getNamespaces();
             foreach ($ns as $key => $value) {
                 $package->registerXPathNamespace($key, $value);
-                $opfFile = (string) $package->xpath('//'. $key .':rootfile/@full-path')[0]['full-path'];
+                $items = $package->xpath('//'. $key .':rootfile/@full-path');
+                $opfFile = (string) $items[0]['full-path'];
             }
         }
 
@@ -61,4 +62,4 @@ public function load($file)
         
         return $package;
     }
-}
\ No newline at end of file
+}