diff --git a/phpBB/includes/functions_upload.php b/phpBB/includes/functions_upload.php
index f3ae9d6cc4..aedf361000 100644
--- a/phpBB/includes/functions_upload.php
+++ b/phpBB/includes/functions_upload.php
@@ -154,7 +154,7 @@ class filespec
 		$finfo = new finfo(FILEINFO_MIME_TYPE);
 		$mimetype = $finfo->file($this->filename);
 
-		return (strpos($mimetype, 'image/') !== false) ? true : false;
+		return (strpos($mimetype, 'image/') === 0);
 	}
 
 	/**