diff --git a/src/cryptonote_core/cryptonote_core.cpp b/src/cryptonote_core/cryptonote_core.cpp
index 63ab899ce..ce75f74d8 100644
--- a/src/cryptonote_core/cryptonote_core.cpp
+++ b/src/cryptonote_core/cryptonote_core.cpp
@@ -81,7 +81,7 @@ namespace cryptonote
   , "Specify data directory"
   , tools::get_default_data_dir()
   , {{ &arg_testnet_on, &arg_stagenet_on }}
-  , [](std::array<bool, 2> testnet_stagenet, bool defaulted, std::string val) {
+  , [](std::array<bool, 2> testnet_stagenet, bool defaulted, std::string val)->std::string {
       if (testnet_stagenet[0])
         return (boost::filesystem::path(val) / "testnet").string();
       else if (testnet_stagenet[1])
diff --git a/src/daemon/command_line_args.h b/src/daemon/command_line_args.h
index add752029..4673590aa 100644
--- a/src/daemon/command_line_args.h
+++ b/src/daemon/command_line_args.h
@@ -42,7 +42,7 @@ namespace daemon_args
   , "Specify configuration file"
   , (daemonizer::get_default_data_dir() / std::string(CRYPTONOTE_NAME ".conf")).string()
   , {{ &cryptonote::arg_testnet_on, &cryptonote::arg_stagenet_on }}
-  , [](std::array<bool, 2> testnet_stagenet, bool defaulted, std::string val) {
+  , [](std::array<bool, 2> testnet_stagenet, bool defaulted, std::string val)->std::string {
       if (testnet_stagenet[0] && defaulted)
         return (daemonizer::get_default_data_dir() / "testnet" /
                 std::string(CRYPTONOTE_NAME ".conf")).string();
@@ -57,7 +57,7 @@ namespace daemon_args
   , "Specify log file"
   , (daemonizer::get_default_data_dir() / std::string(CRYPTONOTE_NAME ".log")).string()
   , {{ &cryptonote::arg_testnet_on, &cryptonote::arg_stagenet_on }}
-  , [](std::array<bool, 2> testnet_stagenet, bool defaulted, std::string val) {
+  , [](std::array<bool, 2> testnet_stagenet, bool defaulted, std::string val)->std::string {
       if (testnet_stagenet[0] && defaulted)
         return (daemonizer::get_default_data_dir() / "testnet" /
                 std::string(CRYPTONOTE_NAME ".log")).string();
@@ -102,7 +102,7 @@ namespace daemon_args
   , "Port for ZMQ RPC server to listen on"
   , std::to_string(config::ZMQ_RPC_DEFAULT_PORT)
   , {{ &cryptonote::arg_testnet_on, &cryptonote::arg_stagenet_on }}
-  , [](std::array<bool, 2> testnet_stagenet, bool defaulted, std::string val) {
+  , [](std::array<bool, 2> testnet_stagenet, bool defaulted, std::string val)->std::string {
       if (testnet_stagenet[0] && defaulted)
         return std::to_string(config::testnet::ZMQ_RPC_DEFAULT_PORT);
       if (testnet_stagenet[1] && defaulted)
diff --git a/src/p2p/net_node.cpp b/src/p2p/net_node.cpp
index bde6fc88e..c9ca63f43 100755
--- a/src/p2p/net_node.cpp
+++ b/src/p2p/net_node.cpp
@@ -39,7 +39,7 @@ namespace nodetool
       , "Port for p2p network protocol"
       , std::to_string(config::P2P_DEFAULT_PORT)
       , {{ &cryptonote::arg_testnet_on, &cryptonote::arg_stagenet_on }}
-      , [](std::array<bool, 2> testnet_stagenet, bool defaulted, std::string val) {
+      , [](std::array<bool, 2> testnet_stagenet, bool defaulted, std::string val)->std::string {
           if (testnet_stagenet[0] && defaulted)
             return std::to_string(config::testnet::P2P_DEFAULT_PORT);
           else if (testnet_stagenet[1] && defaulted)
diff --git a/src/rpc/core_rpc_server.cpp b/src/rpc/core_rpc_server.cpp
index b3bf1ab6e..b8f85da29 100644
--- a/src/rpc/core_rpc_server.cpp
+++ b/src/rpc/core_rpc_server.cpp
@@ -2122,7 +2122,7 @@ namespace cryptonote
     , "Port for RPC server"
     , std::to_string(config::RPC_DEFAULT_PORT)
     , {{ &cryptonote::arg_testnet_on, &cryptonote::arg_stagenet_on }}
-    , [](std::array<bool, 2> testnet_stagenet, bool defaulted, std::string val) {
+    , [](std::array<bool, 2> testnet_stagenet, bool defaulted, std::string val)->std::string {
         if (testnet_stagenet[0] && defaulted)
           return std::to_string(config::testnet::RPC_DEFAULT_PORT);
         else if (testnet_stagenet[1] && defaulted)
diff --git a/src/wallet/wallet2.cpp b/src/wallet/wallet2.cpp
index 13fdf6ab8..ec0c264ce 100755
--- a/src/wallet/wallet2.cpp
+++ b/src/wallet/wallet2.cpp
@@ -145,7 +145,7 @@ struct options {
     "shared-ringdb-dir", tools::wallet2::tr("Set shared ring database path"),
     get_default_ringdb_path(),
     testnet,
-    [](bool testnet, bool defaulted, std::string val) {
+    [](bool testnet, bool defaulted, std::string val)->std::string {
       if (testnet)
         return (boost::filesystem::path(val) / "testnet").string();
       return val;