--- typo3/sysext/cms/tslib/class.tslib_fe.php	(revision 5403)
+++ typo3/sysext/cms/tslib/class.tslib_fe.php	(working copy)
@@ -3342,8 +3342,15 @@
 			}
 		}
 
-			// Send content-lenght header. Notice that all HTML content outside the length of the content-length header will be cut off! Therefore content of unknown length from included PHP-scripts and if admin users are logged in (admin panel might show...) we disable it!
-		if ($this->config['config']['enableContentLengthHeader'] && !$this->isEXTincScript() && !$this->beUserLogin && !$this->doWorkspacePreview())	{
+			// Send content-lenght header.
+			// Notice that all HTML content outside the length of the content-length header will be cut off! Therefore content of unknown length from included PHP-scripts and if admin users are logged in (admin panel might show...) or if debug mode is turned on we disable it!
+		if ($this->config['config']['enableContentLengthHeader'] &&
+			!$this->isEXTincScript() &&
+			!$this->beUserLogin  &&
+			!$this->TYPO3_CONF_VARS['FE']['debug'] &&
+			!$this->config['config']['debug'] &&
+			!$this->doWorkspacePreview()
+		) {
 			header('Content-Length: '.strlen($this->content));
 		}
 	}