diff --git a/tools/python/xen/xend/sxp.py b/tools/python/xen/xend/sxp.py
index c31f8e4d21..c87270f070 100644
--- a/tools/python/xen/xend/sxp.py
+++ b/tools/python/xen/xend/sxp.py
@@ -365,6 +365,8 @@ class Parser:
 def atomp(sxpr):
     """Check if an sxpr is an atom.
     """
+    if sxpr == '':
+        return 0
     if sxpr.isalnum() or sxpr == '@':
         return 1
     for c in sxpr: