diff --git a/check_zfs.py b/check_zfs.py
index 74f0f4a..040d7a5 100755
--- a/check_zfs.py
+++ b/check_zfs.py
@@ -350,7 +350,7 @@ def GetArgsForZfsCommand(zfsCommandAndArgsList):
     stateNum = RaiseStateNum(3, stateNum)
     logging.warning("%s: Missing required field in zpool output: NAME", nagiosStatus[stateNum])
     exit(stateNum)
-if compressValue=='on':
+if compressValue and compressValue!='off':
     getCompressRatioCommand = GetArgsForZfsCommand([zfsCommand, 'get', 'compressratio', args.pool])
 
     try: