diff --git a/poxx.py b/poxx.py
index 92683d5..404a5dc 100755
--- a/poxx.py
+++ b/poxx.py
@@ -67,6 +67,8 @@ def handle_starttag(self, tag, attrs, closed=False):
             if name in ['alt', 'title']:
                 self.s += self.xform(val)
             else:
+                if val is None:
+                    val = ""
                 self.s += val
             self.s += '"'
         if closed: