diff --git a/htdocs/core/class/html.formfile.class.php b/htdocs/core/class/html.formfile.class.php
index 9c0968436d3..172d65b4ca6 100644
--- a/htdocs/core/class/html.formfile.class.php
+++ b/htdocs/core/class/html.formfile.class.php
@@ -796,7 +796,7 @@ class FormFile
 					{
 						print '<td align="center">';
 						$tmp=explode('.',$file['name']);
-						$minifile=$tmp[0].'_mini.'.$tmp[1];
+						$minifile=$tmp[0].'_mini.'.strtolower($tmp[1]);	// Thumbs are created with filename in lower case
 						if (image_format_supported($file['name']) > 0) print '<img border="0" height="'.$maxheightmini.'" src="'.DOL_URL_ROOT.'/viewimage.php?modulepart='.$modulepart.'&file='.urlencode($relativepath.'thumbs/'.$minifile).'" title="">';
 						else print '&nbsp;';
 						print '</td>';