diff --git a/phpBB/includes/functions_upload.php b/phpBB/includes/functions_upload.php
index f70e20e616..d4c6b42cf4 100644
--- a/phpBB/includes/functions_upload.php
+++ b/phpBB/includes/functions_upload.php
@@ -151,7 +151,7 @@ class filespec
 	*/
 	function is_image()
 	{
-		return (strpos($this->mimetype, 'image/') !== false) ? true : false;
+		return (strpos($this->mimetype, 'image/') === 0);
 	}
 
 	/**