Use CI's is_php() instead of comparing against phpversion()
diff --git a/system/libraries/Upload.php b/system/libraries/Upload.php
index 67551fb..fc3de03 100644
--- a/system/libraries/Upload.php
+++ b/system/libraries/Upload.php
@@ -1021,7 +1021,7 @@
protected function _file_mime_type($file)
{
// Use if the Fileinfo extension, if available (only versions above 5.3 support the FILEINFO_MIME_TYPE flag)
- if ( (float) substr(phpversion(), 0, 3) >= 5.3 && function_exists('finfo_file'))
+ if (is_php('5.3') && function_exists('finfo_file'))
{
$finfo = new finfo(FILEINFO_MIME_TYPE);
if ($finfo !== FALSE) // This is possible, if there is no magic MIME database file found on the system