diff --git a/lib/cmdlib.py b/lib/cmdlib.py
index eefb44f59fad2fa5217313086f07463c96a123bc..c7370c7608be7fa090668b747d2189835df009e0 100644
--- a/lib/cmdlib.py
+++ b/lib/cmdlib.py
@@ -3334,7 +3334,7 @@ class LUCreateInstance(LogicalUnit):
     self.check_ip = hostname1.ip
 
     # MAC address verification
-    if self.op.mac != "auto":
+    if self.op.mac not in (constants.VALUE_AUTO, constants.VALUE_GENERATE):
       if not utils.IsValidMac(self.op.mac.lower()):
         raise errors.OpPrereqError("invalid MAC address specified: %s" %
                                    self.op.mac)
@@ -3588,7 +3588,7 @@ class LUCreateInstance(LogicalUnit):
     instance = self.op.instance_name
     pnode_name = self.pnode.name
 
-    if self.op.mac == "auto":
+    if self.op.mac in (constants.VALUE_AUTO, constants.VALUE_GENERATE):
       mac_address = self.cfg.GenerateMAC()
     else:
       mac_address = self.op.mac