diff --git a/admin/js/pagedown.js b/admin/js/pagedown.js
index 6f10168a..f085edbc 100644
--- a/admin/js/pagedown.js
+++ b/admin/js/pagedown.js
@@ -2877,7 +2877,9 @@ else
             else {
                 // Fixes common pasting errors.
                 text = text.replace(/^http:\/\/(https?|ftp):\/\//, '$1://');
-                if (!/^(?:https?|ftp):\/\//.test(text))
+
+                // fix issue #552
+                if (!/^(?:https?|ftp):\/\//.test(text) && !/^[_a-z0-9-]+:/i.test(text))
                     text = 'http://' + text;
             }