diff --git a/compare_and_swap.go b/compare_and_swap.go
index 2b63751..e34e11e 100644
--- a/compare_and_swap.go
+++ b/compare_and_swap.go
@@ -6,16 +6,16 @@ import (
 )
 
 const CompareAndSwapUsage = `usage: etcdctl [etcd flags] compareAndSwap <key> <value> [testAndSet flags]
-either prevValue or prevIndex needs to be given
+either prevvalue or previndex needs to be given
 special flags: --ttl to set a key with ttl
-			   --prevValue to set the previous value
-			   --prevIndex to set the previous index`
+			   --prevvalue to set the previous value
+			   --previndex to set the previous index`
 
 var (
 	compareAndSwapFlag   = flag.NewFlagSet("testAndSet", flag.ExitOnError)
 	compareAndSwapTtl    = compareAndSwapFlag.Uint64("ttl", 0, "ttl of the key")
-	compareAndSwapPvalue = compareAndSwapFlag.String("prevValue", "", "previous value")
-	compareAndSwapPindex = compareAndSwapFlag.Uint64("prevIndex", 0, "previous index")
+	compareAndSwapPvalue = compareAndSwapFlag.String("prevvalue", "", "previous value")
+	compareAndSwapPindex = compareAndSwapFlag.Uint64("previndex", 0, "previous index")
 )
 
 func init() {