diff --git a/dom0/qvm-core/qubes.py b/dom0/qvm-core/qubes.py
index 16f0379a..0a78f62b 100755
--- a/dom0/qvm-core/qubes.py
+++ b/dom0/qvm-core/qubes.py
@@ -1066,7 +1066,7 @@ class QubesVm(object):
                     rule["netmask"] = 32
 
                 # For backward compatibility default to tcp
-                if rule["proto" is None:
+                if rule["proto"] is None:
                     rule["proto"] = "tcp"
 
                 if rule["port"] is not None: