diff --git a/etcd/v3/Transaction.hpp b/etcd/v3/Transaction.hpp
index bc561b8..a438b1b 100644
--- a/etcd/v3/Transaction.hpp
+++ b/etcd/v3/Transaction.hpp
@@ -30,6 +30,9 @@ public:
 	Transaction();
 	Transaction(std::string const&);
 	virtual ~Transaction();
+
+	void set_key(std::string const& comp_key);
+
 	void init_compare(CompareResult, CompareTarget);
 	void init_compare(std::string const &old_value, CompareResult, CompareTarget);
 	void init_compare(int old_value, CompareResult, CompareTarget);
diff --git a/src/v3/Transaction.cpp b/src/v3/Transaction.cpp
index 52aba99..7dbc8b8 100644
--- a/src/v3/Transaction.cpp
+++ b/src/v3/Transaction.cpp
@@ -32,6 +32,10 @@ etcdv3::Transaction::Transaction(const std::string& key) : key(key) {
 	txn_request.reset(new etcdserverpb::TxnRequest{});
 }
 
+void etcdv3::set_key(std::string const& comp_key) {
+	key = comp_key;
+}
+
 void etcdv3::Transaction::init_compare(CompareResult result, CompareTarget target){
 	Compare* compare = txn_request->add_compare();
 	compare->set_result(detail::to_compare_result(result));