diff --git a/CRM/Mosaico/Utils.php b/CRM/Mosaico/Utils.php
index ca3b61a1b..0f23f60d2 100644
--- a/CRM/Mosaico/Utils.php
+++ b/CRM/Mosaico/Utils.php
@@ -431,7 +431,9 @@ public static function sendImage(string $file) {
     header("Content-type:" . $mime_type);
 
     readfile($file);
-    ob_flush();
+    if (ob_get_length()) {
+      ob_flush();
+    }
     flush();
   }