diff --git a/CMakeLists.txt b/CMakeLists.txt
index d5d3ab2..ad1bfa7 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -28,6 +28,7 @@ add_executable(FlashMQ
     configfileparser.cpp
     sslctxmanager.cpp
     timer.cpp
+    globalsettings.cpp
     )
 
 target_link_libraries(FlashMQ pthread dl ssl crypto)
diff --git a/configfileparser.cpp b/configfileparser.cpp
index b9cc8b7..f6acf16 100644
--- a/configfileparser.cpp
+++ b/configfileparser.cpp
@@ -98,6 +98,7 @@ ConfigFileParser::ConfigFileParser(const std::string &path) :
     validKeys.insert("ssl_listen_port");
     validKeys.insert("fullchain");
     validKeys.insert("privkey");
+    validKeys.insert("allow_unsafe_clientid_chars");
 }
 
 void ConfigFileParser::loadFile(bool test)
@@ -192,6 +193,13 @@ void ConfigFileParser::loadFile(bool test)
                     this->logPath = value;
             }
 
+            if (key == "allow_unsafe_clientid_chars")
+            {
+                bool tmp = stringTruthiness(value);
+                if (!test)
+                    this->allowUnsafeClientidChars = tmp;
+            }
+
             if (key == "fullchain")
             {
                 checkFileAccess(key, value);
diff --git a/configfileparser.h b/configfileparser.h
index abebdeb..bb4529a 100644
--- a/configfileparser.h
+++ b/configfileparser.h
@@ -54,6 +54,7 @@ public:
     std::string sslPrivkey;
     uint listenPort = 1883;
     uint sslListenPort = 0;
+    bool allowUnsafeClientidChars = false;
 };
 
 #endif // CONFIGFILEPARSER_H
diff --git a/globalsettings.cpp b/globalsettings.cpp
new file mode 100644
index 0000000..e559a67
--- /dev/null
+++ b/globalsettings.cpp
@@ -0,0 +1,16 @@
+#include "globalsettings.h"
+
+GlobalSettings *GlobalSettings::instance = nullptr;
+
+GlobalSettings::GlobalSettings()
+{
+
+}
+
+GlobalSettings *GlobalSettings::getInstance()
+{
+    if (instance == nullptr)
+        instance = new GlobalSettings();
+
+    return instance;
+}
diff --git a/globalsettings.h b/globalsettings.h
new file mode 100644
index 0000000..14fed52
--- /dev/null
+++ b/globalsettings.h
@@ -0,0 +1,14 @@
+#ifndef GLOBALSETTINGS_H
+#define GLOBALSETTINGS_H
+
+// 'Global' as in, needed outside of the mainapp, like listen ports.
+class GlobalSettings
+{
+    static GlobalSettings *instance;
+    GlobalSettings();
+public:
+    static GlobalSettings *getInstance();
+
+    bool allow_unsafe_clientid_chars = false;
+};
+#endif // GLOBALSETTINGS_H
diff --git a/mainapp.cpp b/mainapp.cpp
index 5d49326..6bb8bf8 100644
--- a/mainapp.cpp
+++ b/mainapp.cpp
@@ -453,6 +453,7 @@ void MainApp::quit()
 void MainApp::loadConfig()
 {
     Logger *logger = Logger::getInstance();
+    GlobalSettings *setting = GlobalSettings::getInstance();
 
     // Atomic loading, first test.
     confFileParser->loadFile(true);
@@ -471,6 +472,8 @@ void MainApp::loadConfig()
         SSL_CTX_set_options(sslctx, SSL_OP_NO_TLSv1); // TODO: config option
     }
 
+    setting->allow_unsafe_clientid_chars = confFileParser->allowUnsafeClientidChars;
+
     setCertAndKeyFromConfig();
 }
 
diff --git a/mainapp.h b/mainapp.h
index 413ca7d..97b6746 100644
--- a/mainapp.h
+++ b/mainapp.h
@@ -20,6 +20,7 @@
 #include "subscriptionstore.h"
 #include "configfileparser.h"
 #include "timer.h"
+#include "globalsettings.h"
 
 class MainApp
 {
@@ -63,7 +64,7 @@ public:
     bool getStarted() const {return started;}
     static void testConfig();
 
-
+    GlobalSettings &getGlobalSettings();
     void queueConfigReload();
     void queueCleanup();
 };
diff --git a/mqttpacket.cpp b/mqttpacket.cpp
index 79b781b..b8080ef 100644
--- a/mqttpacket.cpp
+++ b/mqttpacket.cpp
@@ -153,6 +153,8 @@ void MqttPacket::handleConnect()
     if (sender->hasConnectPacketSeen())
         throw ProtocolError("Client already sent a CONNECT.");
 
+    GlobalSettings *settings = GlobalSettings::getInstance();
+
     uint16_t variable_header_length = readTwoBytesToUInt16();
 
     if (variable_header_length == 4 || variable_header_length == 6)
@@ -240,10 +242,9 @@ void MqttPacket::handleConnect()
         bool validClientId = true;
 
         // Check for wildcard chars in case the client_id ever appears in topics.
-        // TODO: make setting?
-        if (strContains(client_id, "+") || strContains(client_id, "#"))
+        if (!settings->allow_unsafe_clientid_chars && (strContains(client_id, "+") || strContains(client_id, "#")))
         {
-            logger->logf(LOG_ERR, "ClientID '%s' has + or # in the id:", client_id.c_str());
+            logger->logf(LOG_ERR, "ClientID '%s' has + or # in the id and 'allow_unsafe_clientid_chars' is false:", client_id.c_str());
             validClientId = false;
         }
         else if (!clean_session && client_id.empty())
@@ -261,6 +262,7 @@ void MqttPacket::handleConnect()
         {
             ConnAck connAck(ConnAckReturnCodes::ClientIdRejected);
             MqttPacket response(connAck);
+            sender->setDisconnectReason("Invalid clientID");
             sender->setReadyForDisconnect();
             sender->writeMqttPacket(response);
             return;
@@ -288,6 +290,7 @@ void MqttPacket::handleConnect()
         {
             ConnAck connDeny(ConnAckReturnCodes::NotAuthorized);
             MqttPacket response(connDeny);
+            sender->setDisconnectReason("Access denied");
             sender->setReadyForDisconnect();
             sender->writeMqttPacket(response);
             logger->logf(LOG_NOTICE, "User '%s' access denied", username.c_str());
diff --git a/mqttpacket.h b/mqttpacket.h
index 92d85dd..2f4c86a 100644
--- a/mqttpacket.h
+++ b/mqttpacket.h
@@ -14,6 +14,8 @@
 #include "subscriptionstore.h"
 #include "cirbuf.h"
 #include "logger.h"
+#include "mainapp.h"
+#include "globalsettings.h"
 
 struct RemainingLength
 {
diff --git a/utils.cpp b/utils.cpp
index baf8c46..17be781 100644
--- a/utils.cpp
+++ b/utils.cpp
@@ -203,3 +203,21 @@ std::string getSecureRandomString(const size_t len)
     }
     return randomString;
 }
+
+std::string str_tolower(std::string s)
+{
+    std::transform(s.begin(), s.end(), s.begin(),
+                   [](unsigned char c){ return std::tolower(c); });
+    return s;
+}
+
+bool stringTruthiness(const std::string &val)
+{
+    std::string val_ = str_tolower(val);
+    trim(val_);
+    if (val_ == "yes" || val_ == "true" || val_ == "on")
+        return  true;
+    if (val_ == "no" || val_ == "false" || val_ == "off")
+        return false;
+    throw ConfigFileException("Value '" + val + "' can't be converted to boolean");
+}
diff --git a/utils.h b/utils.h
index 6862146..b1161bc 100644
--- a/utils.h
+++ b/utils.h
@@ -39,5 +39,7 @@ bool startsWith(const std::string &s, const std::string &needle);
 
 int64_t currentMSecsSinceEpoch();
 std::string getSecureRandomString(const size_t len);
+std::string str_tolower(std::string s);
+bool stringTruthiness(const std::string &val);
 
 #endif // UTILS_H