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;
 	}
 
 	// --------------------------------------------------------------------
diff --git a/user_guide_src/source/changelog.rst b/user_guide_src/source/changelog.rst
index 766cb31..5c233ef 100644
--- a/user_guide_src/source/changelog.rst
+++ b/user_guide_src/source/changelog.rst
@@ -306,6 +306,7 @@
       -  Added a ``$reset`` parameter to method ``initialize()``.
       -  Removed method ``clean_file_name()`` and its usage in favor of :doc:`Security Library <libraries/security>`'s ``sanitize_filename()``.
       -  Removed method ``mimes_types()``.
+      -  Changed ``CI_Upload::_prep_filename()`` to simply replace all (but the last) dots in the filename with underscores, instead of suffixing them.
 
    -  :doc:`Calendar Library <libraries/calendar>` changes include: