diff --git a/src/Mouf/Html/Template/BootstrapTemplate.php b/src/Mouf/Html/Template/BootstrapTemplate.php
index d73615b..10308ab 100644
--- a/src/Mouf/Html/Template/BootstrapTemplate.php
+++ b/src/Mouf/Html/Template/BootstrapTemplate.php
@@ -123,7 +123,7 @@ public function toHtml()
         // Let's register the template renderer in the default renderer.
         $this->getDefaultRenderer()->setTemplateRendererInstanceName($this->getTemplateRendererInstanceName());
 
-        if (PHP_SAPI !== 'cli') {
+        if (PHP_SAPI !== 'cli' && !headers_sent()) {
             header('Content-Type: text/html; charset=utf-8');
         }
         //Renderable::toHtml();// __DIR__."/../../../../views/template.php";