diff --git a/library/Icinga/File/Csv.php b/library/Icinga/File/Csv.php
index 56ee233eeb..d189780403 100644
--- a/library/Icinga/File/Csv.php
+++ b/library/Icinga/File/Csv.php
@@ -37,7 +37,7 @@ public function __toString()
             }
             $out = array();
             foreach ($row as & $val) {
-                $out[] = '"' . str_replace('"', '""', $val) . '"';
+                $out[] = '"' . ($val ? str_replace('"', '""', $val) : '') . '"';
             }
             $csv .= implode(',', $out) . "\r\n";
         }