diff --git a/phpBB/includes/functions_posting.php b/phpBB/includes/functions_posting.php
index 51c69761fc..85f2089628 100644
--- a/phpBB/includes/functions_posting.php
+++ b/phpBB/includes/functions_posting.php
@@ -686,6 +686,10 @@ function create_thumbnail($source, $destination, $mimetype)
 					return false;
 				}
 
+				// Preserve alpha transparency (png for example)
+				@imagealphablending($new_image, false);
+				@imagesavealpha($new_image, true);
+
 				imagecopyresampled($new_image, $image, 0, 0, 0, 0, $new_width, $new_height, $width, $height);
 			}