diff --git a/src/net_permissions.cpp b/src/net_permissions.cpp
index 5f5e0ee8a3..42b4bc7b57 100644
--- a/src/net_permissions.cpp
+++ b/src/net_permissions.cpp
@@ -10,8 +10,8 @@
 
 namespace {
 
-// The parse the following format "perm1,perm2@xxxxxx"
-bool TryParsePermissionFlags(const std::string str, NetPermissionFlags& output, size_t& readen, bilingual_str& error)
+// Parse the following format: "perm1,perm2@xxxxxx"
+bool TryParsePermissionFlags(const std::string& str, NetPermissionFlags& output, size_t& readen, bilingual_str& error)
 {
     NetPermissionFlags flags = PF_NONE;
     const auto atSeparator = str.find('@');
@@ -67,7 +67,7 @@ std::vector<std::string> NetPermissions::ToStrings(NetPermissionFlags flags)
     return strings;
 }
 
-bool NetWhitebindPermissions::TryParse(const std::string str, NetWhitebindPermissions& output, bilingual_str& error)
+bool NetWhitebindPermissions::TryParse(const std::string& str, NetWhitebindPermissions& output, bilingual_str& error)
 {
     NetPermissionFlags flags;
     size_t offset;
@@ -90,7 +90,7 @@ bool NetWhitebindPermissions::TryParse(const std::string str, NetWhitebindPermis
     return true;
 }
 
-bool NetWhitelistPermissions::TryParse(const std::string str, NetWhitelistPermissions& output, bilingual_str& error)
+bool NetWhitelistPermissions::TryParse(const std::string& str, NetWhitelistPermissions& output, bilingual_str& error)
 {
     NetPermissionFlags flags;
     size_t offset;
diff --git a/src/net_permissions.h b/src/net_permissions.h
index 3edbdeea4d..789c417808 100644
--- a/src/net_permissions.h
+++ b/src/net_permissions.h
@@ -51,14 +51,14 @@ public:
 class NetWhitebindPermissions : public NetPermissions
 {
 public:
-    static bool TryParse(const std::string str, NetWhitebindPermissions& output, bilingual_str& error);
+    static bool TryParse(const std::string& str, NetWhitebindPermissions& output, bilingual_str& error);
     CService m_service;
 };
 
 class NetWhitelistPermissions : public NetPermissions
 {
 public:
-    static bool TryParse(const std::string str, NetWhitelistPermissions& output, bilingual_str& error);
+    static bool TryParse(const std::string& str, NetWhitelistPermissions& output, bilingual_str& error);
     CSubNet m_subnet;
 };
 
diff --git a/src/ui_interface.cpp b/src/ui_interface.cpp
index bd2b7284f6..20afbe0639 100644
--- a/src/ui_interface.cpp
+++ b/src/ui_interface.cpp
@@ -6,14 +6,14 @@
 
 #include <util/translation.h>
 
-#include <boost/signals2/last_value.hpp>
+#include <boost/signals2/optional_last_value.hpp>
 #include <boost/signals2/signal.hpp>
 
 CClientUIInterface uiInterface;
 
 struct UISignals {
-    boost::signals2::signal<CClientUIInterface::ThreadSafeMessageBoxSig, boost::signals2::last_value<bool>> ThreadSafeMessageBox;
-    boost::signals2::signal<CClientUIInterface::ThreadSafeQuestionSig, boost::signals2::last_value<bool>> ThreadSafeQuestion;
+    boost::signals2::signal<CClientUIInterface::ThreadSafeMessageBoxSig, boost::signals2::optional_last_value<bool>> ThreadSafeMessageBox;
+    boost::signals2::signal<CClientUIInterface::ThreadSafeQuestionSig, boost::signals2::optional_last_value<bool>> ThreadSafeQuestion;
     boost::signals2::signal<CClientUIInterface::InitMessageSig> InitMessage;
     boost::signals2::signal<CClientUIInterface::NotifyNumConnectionsChangedSig> NotifyNumConnectionsChanged;
     boost::signals2::signal<CClientUIInterface::NotifyNetworkActiveChangedSig> NotifyNetworkActiveChanged;
@@ -50,8 +50,8 @@ ADD_SIGNALS_IMPL_WRAPPER(NotifyMasternodeListChanged);
 ADD_SIGNALS_IMPL_WRAPPER(NotifyAdditionalDataSyncProgressChanged);
 ADD_SIGNALS_IMPL_WRAPPER(BannedListChanged);
 
-bool CClientUIInterface::ThreadSafeMessageBox(const bilingual_str& message, const std::string& caption, unsigned int style) { return g_ui_signals.ThreadSafeMessageBox(message, caption, style); }
-bool CClientUIInterface::ThreadSafeQuestion(const bilingual_str& message, const std::string& non_interactive_message, const std::string& caption, unsigned int style) { return g_ui_signals.ThreadSafeQuestion(message, non_interactive_message, caption, style); }
+bool CClientUIInterface::ThreadSafeMessageBox(const bilingual_str& message, const std::string& caption, unsigned int style) { return g_ui_signals.ThreadSafeMessageBox(message, caption, style).value_or(false);}
+bool CClientUIInterface::ThreadSafeQuestion(const bilingual_str& message, const std::string& non_interactive_message, const std::string& caption, unsigned int style) { return g_ui_signals.ThreadSafeQuestion(message, non_interactive_message, caption, style).value_or(false);}
 void CClientUIInterface::InitMessage(const std::string& message) { return g_ui_signals.InitMessage(message); }
 void CClientUIInterface::NotifyNumConnectionsChanged(int newNumConnections) { return g_ui_signals.NotifyNumConnectionsChanged(newNumConnections); }
 void CClientUIInterface::NotifyNetworkActiveChanged(bool networkActive) { return g_ui_signals.NotifyNetworkActiveChanged(networkActive); }
diff --git a/src/ui_interface.h b/src/ui_interface.h
index b03df680ee..beed4d431d 100644
--- a/src/ui_interface.h
+++ b/src/ui_interface.h
@@ -139,7 +139,7 @@ void InitWarning(const bilingual_str& str);
 
 /** Show error message **/
 bool InitError(const bilingual_str& str);
-constexpr auto AbortError = InitError;
+inline bool AbortError(const bilingual_str& str) { return InitError(str); }
 
 extern CClientUIInterface uiInterface;
 
diff --git a/test/lint/lint-includes.sh b/test/lint/lint-includes.sh
index e8c0ead871..74b4f9bdfd 100755
--- a/test/lint/lint-includes.sh
+++ b/test/lint/lint-includes.sh
@@ -67,7 +67,7 @@ EXPECTED_BOOST_INCLUDES=(
     boost/preprocessor/cat.hpp
     boost/preprocessor/stringize.hpp
     boost/signals2/connection.hpp
-    boost/signals2/last_value.hpp
+    boost/signals2/optional_last_value.hpp
     boost/signals2/signal.hpp
     boost/test/unit_test.hpp
     boost/thread.hpp