diff --git a/src/mqtt/MQTT.cpp b/src/mqtt/MQTT.cpp
index 5e32050ad..b03ae3579 100644
--- a/src/mqtt/MQTT.cpp
+++ b/src/mqtt/MQTT.cpp
@@ -17,9 +17,9 @@
 
 MQTT *mqtt;
 
-String statusTopic = "msh/2/stat/";
-String cryptTopic = "msh/2/c/";   // msh/2/c/CHANNELID/NODEID
-String jsonTopic = "msh/2/json/"; // msh/2/json/CHANNELID/NODEID
+std::string statusTopic = "msh/2/stat/";
+std::string cryptTopic = "msh/2/c/";   // msh/2/c/CHANNELID/NODEID
+std::string jsonTopic = "msh/2/json/"; // msh/2/json/CHANNELID/NODEID
 
 static MemoryDynamic<meshtastic_ServiceEnvelope> staticMqttPool;
 
@@ -238,11 +238,11 @@ void MQTT::sendSubscriptions()
     for (size_t i = 0; i < numChan; i++) {
         auto &ch = channels.getByIndex(i);
         if (ch.settings.downlink_enabled) {
-            String topic = cryptTopic + channels.getGlobalId(i) + "/#";
+            std::string topic = cryptTopic + channels.getGlobalId(i) + "/#";
             LOG_INFO("Subscribing to %s\n", topic.c_str());
             pubSub.subscribe(topic.c_str(), 1); // FIXME, is QOS 1 right?
             if (moduleConfig.mqtt.json_enabled == true) {
-                String topicDecoded = jsonTopic + channels.getGlobalId(i) + "/#";
+                std::string topicDecoded = jsonTopic + channels.getGlobalId(i) + "/#";
                 LOG_INFO("Subscribing to %s\n", topicDecoded.c_str());
                 pubSub.subscribe(topicDecoded.c_str(), 1); // FIXME, is QOS 1 right?
             }
@@ -296,7 +296,7 @@ int32_t MQTT::runOnce()
                     static uint8_t bytes[meshtastic_MeshPacket_size + 64];
                     size_t numBytes = pb_encode_to_bytes(bytes, sizeof(bytes), &meshtastic_ServiceEnvelope_msg, env);
 
-                    String topic = cryptTopic + env->channel_id + "/" + owner.id;
+                    std::string topic = cryptTopic + env->channel_id + "/" + owner.id;
                     LOG_INFO("publish %s, %u bytes from queue\n", topic.c_str(), numBytes);
 
                     pubSub.publish(topic.c_str(), bytes, numBytes, false);
@@ -305,7 +305,7 @@ int32_t MQTT::runOnce()
                         // handle json topic
                         auto jsonString = this->downstreamPacketToJson(env->packet);
                         if (jsonString.length() != 0) {
-                            String topicJson = jsonTopic + env->channel_id + "/" + owner.id;
+                            std::string topicJson = jsonTopic + env->channel_id + "/" + owner.id;
                             LOG_INFO("JSON publish message to %s, %u bytes: %s\n", topicJson.c_str(), jsonString.length(),
                                      jsonString.c_str());
                             pubSub.publish(topicJson.c_str(), jsonString.c_str(), false);
@@ -350,7 +350,7 @@ void MQTT::onSend(const meshtastic_MeshPacket &mp, ChannelIndex chIndex)
             static uint8_t bytes[meshtastic_MeshPacket_size + 64];
             size_t numBytes = pb_encode_to_bytes(bytes, sizeof(bytes), &meshtastic_ServiceEnvelope_msg, env);
 
-            String topic = cryptTopic + channelId + "/" + owner.id;
+            std::string topic = cryptTopic + channelId + "/" + owner.id;
             LOG_DEBUG("publish %s, %u bytes\n", topic.c_str(), numBytes);
 
             pubSub.publish(topic.c_str(), bytes, numBytes, false);
@@ -359,7 +359,7 @@ void MQTT::onSend(const meshtastic_MeshPacket &mp, ChannelIndex chIndex)
                 // handle json topic
                 auto jsonString = this->downstreamPacketToJson((meshtastic_MeshPacket *)&mp);
                 if (jsonString.length() != 0) {
-                    String topicJson = jsonTopic + channelId + "/" + owner.id;
+                    std::string topicJson = jsonTopic + channelId + "/" + owner.id;
                     LOG_INFO("JSON publish message to %s, %u bytes: %s\n", topicJson.c_str(), jsonString.length(),
                              jsonString.c_str());
                     pubSub.publish(topicJson.c_str(), jsonString.c_str(), false);
@@ -386,7 +386,7 @@ std::string MQTT::downstreamPacketToJson(meshtastic_MeshPacket *mp)
 {
     // the created jsonObj is immutable after creation, so
     // we need to do the heavy lifting before assembling it.
-    String msgType;
+    std::string msgType;
     JSONObject msgPayload;
     JSONObject jsonObj;