diff --git a/application/Espo/Core/Mail/Account/FetchData.php b/application/Espo/Core/Mail/Account/FetchData.php
index ec102fbebc..fa505bd3fd 100644
--- a/application/Espo/Core/Mail/Account/FetchData.php
+++ b/application/Espo/Core/Mail/Account/FetchData.php
@@ -67,6 +67,11 @@ class FetchData
             return null;
         }
 
+        // For backward compatibility.
+        if ($value === 0) {
+            return null;
+        }
+
         if (!is_string($value)) {
             throw new RuntimeException("Bad value in fetch-data.");
         }