diff --git a/src/Mouf/Html/Template/BootstrapTemplate.php b/src/Mouf/Html/Template/BootstrapTemplate.php
index 240e615..63afd6e 100644
--- a/src/Mouf/Html/Template/BootstrapTemplate.php
+++ b/src/Mouf/Html/Template/BootstrapTemplate.php
@@ -135,7 +135,7 @@ public function toHtml()
         // Let's register the template renderer in the default renderer.
         $this->getDefaultRenderer()->setTemplateRenderer($this->getTemplateRenderer());
 
-        if (PHP_SAPI !== 'cli') {
+        if (PHP_SAPI !== 'cli' && !headers_sent()) {
             header('Content-Type: text/html; charset=utf-8');
         }
         //Renderable::toHtml();// __DIR__."/../../../../views/template.php";