diff --git a/tools/python/xen/util/xsm/acm/acm.py b/tools/python/xen/util/xsm/acm/acm.py
index 52f6ad6333..d58652e06c 100644
--- a/tools/python/xen/util/xsm/acm/acm.py
+++ b/tools/python/xen/util/xsm/acm/acm.py
@@ -1309,7 +1309,7 @@ def parse_security_label(security_label):
         return security_label
 
 def set_security_label(policy, label):
-    if label != "" and policy != "":
+    if label and policy and label != "" and policy != "":
         return "%s:%s:%s" % (xsconstants.ACM_POLICY_ID, policy, label)
     else:
         return ""