diff --git a/system/libraries/Upload.php b/system/libraries/Upload.php
index 7946111..49c69a3 100644
--- a/system/libraries/Upload.php
+++ b/system/libraries/Upload.php
@@ -1158,28 +1158,14 @@
 	 */
 	protected function _prep_filename($filename)
 	{
-		if ($this->mod_mime_fix === FALSE OR $this->allowed_types === '*' OR strpos($filename, '.') === FALSE)
+		if ($this->mod_mime_fix === FALSE OR $this->allowed_types === '*' OR ($ext_pos = strrpos($filename, '.')) === FALSE)
 		{
 			return $filename;
 		}
 
-		$parts		= explode('.', $filename);
-		$ext		= array_pop($parts);
-		$filename	= array_shift($parts);
-
-		foreach ($parts as $part)
-		{
-			if ( ! in_array(strtolower($part), $this->allowed_types) OR ! isset($this->_mimes[strtolower($part)]))
-			{
-				$filename .= '.'.$part.'_';
-			}
-			else
-			{
-				$filename .= '.'.$part;
-			}
-		}
-
-		return $filename.'.'.$ext;
+		$ext = substr($filename, $ext_pos);
+		$filename = substr($filename, 0, $ext_pos);
+		return str_replace('.', '_', $filename).$ext;
 	}
 
 	// --------------------------------------------------------------------