diff --git a/api/kv.go b/api/kv.go
index 867592490..44e06bbb4 100644
--- a/api/kv.go
+++ b/api/kv.go
@@ -50,21 +50,21 @@ type KVOp string
 
 const (
 	KVSet          KVOp = "set"
-	KVDelete            = "delete"
-	KVDeleteCAS         = "delete-cas"
-	KVDeleteTree        = "delete-tree"
-	KVCAS               = "cas"
-	KVLock              = "lock"
-	KVUnlock            = "unlock"
-	KVGet               = "get"
-	KVGetTree           = "get-tree"
-	KVCheckSession      = "check-session"
-	KVCheckIndex        = "check-index"
+	KVDelete       KVOp = "delete"
+	KVDeleteCAS    KVOp = "delete-cas"
+	KVDeleteTree   KVOp = "delete-tree"
+	KVCAS          KVOp = "cas"
+	KVLock         KVOp = "lock"
+	KVUnlock       KVOp = "unlock"
+	KVGet          KVOp = "get"
+	KVGetTree      KVOp = "get-tree"
+	KVCheckSession KVOp = "check-session"
+	KVCheckIndex   KVOp = "check-index"
 )
 
 // KVTxnOp defines a single operation inside a transaction.
 type KVTxnOp struct {
-	Verb    string
+	Verb    KVOp
 	Key     string
 	Value   []byte
 	Flags   uint64