Fix #1937
diff --git a/system/core/Output.php b/system/core/Output.php
index e969ba8..3bb8f8d 100644
--- a/system/core/Output.php
+++ b/system/core/Output.php
@@ -188,7 +188,7 @@
* @param bool $replace Whether to replace the old header value, if already set
* @return object $this
*/
- public function set_header($header, $replace)
+ public function set_header($header, $replace = TRUE)
{
// If zlib.output_compression is enabled it will compress the output,
// but it will not modify the content-length header to compensate for