diff --git a/client/src/cmdmqtt.c b/client/src/cmdmqtt.c
index f7927da74..51bae4cd6 100644
--- a/client/src/cmdmqtt.c
+++ b/client/src/cmdmqtt.c
@@ -305,24 +305,24 @@ static int CmdMqttSend(const char *Cmd) {
     }
 
     if (alen == 0) {
-        if (strlen(g_session.mqtt_server)) {
-            strcpy(addr, g_session.mqtt_server);
+        if ((g_session.mqtt_server != NULL) && (strcmp(g_session.mqtt_server, "") != 0)) {
+            snprintf(addr, sizeof(addr), "%s", g_session.mqtt_server);
         } else {
             strcpy(addr, "mqtt.proxdump.com");
         }
     }
 
     if (plen == 0) {
-        if (strlen(g_session.mqtt_port)) {
-            strcpy(port, g_session.mqtt_port);
+        if ((g_session.mqtt_port != NULL) && (strcmp(g_session.mqtt_port, "") != 0)) {
+            snprintf(port, sizeof(port), "%s", g_session.mqtt_port);
         } else {
             strcpy(port, "1883");
         }
     }
 
     if (tlen == 0) {
-        if (strlen(g_session.mqtt_topic)) {
-            strcpy(topic, g_session.mqtt_topic);
+        if ((g_session.mqtt_topic != NULL) && (strcmp(g_session.mqtt_topic, "") != 0)) {
+            snprintf(topic, sizeof(topic), "%s", g_session.mqtt_topic);
         } else {
             strcpy(topic, "proxdump");
         }
@@ -382,24 +382,24 @@ static int CmdMqttReceive(const char *Cmd) {
     }
 
     if (alen == 0) {
-        if (strlen(g_session.mqtt_server)) {
-            strcpy(addr, g_session.mqtt_server);
+        if ((g_session.mqtt_server != NULL) && (strcmp(g_session.mqtt_server, "") != 0)) {
+            snprintf(addr, sizeof(addr), "%s", g_session.mqtt_server);
         } else {
             strcpy(addr, "proxdump.com");
         }
     }
 
     if (plen == 0) {
-        if (strlen(g_session.mqtt_port)) {
-            strcpy(port, g_session.mqtt_port);
+        if ((g_session.mqtt_port != NULL) && (strcmp(g_session.mqtt_port, "") != 0)) {
+            snprintf(port, sizeof(port), "%s", g_session.mqtt_port);
         } else {
             strcpy(port, "1883");
         }
     }
 
     if (tlen == 0) {
-        if (strlen(g_session.mqtt_topic)) {
-            strcpy(topic, g_session.mqtt_topic);
+        if ((g_session.mqtt_topic != NULL) && (strcmp(g_session.mqtt_topic, "") != 0)) {
+            snprintf(topic, sizeof(topic), "%s", g_session.mqtt_topic);
         } else {
             strcpy(topic, "proxdump");
         }
diff --git a/client/src/preferences.c b/client/src/preferences.c
index dafb7e7b9..5fd47fd0e 100644
--- a/client/src/preferences.c
+++ b/client/src/preferences.c
@@ -61,9 +61,9 @@ static  bool setDefaultMqttServer(const char *srv) {
 
     char *tmp = (char *)realloc(g_session.mqtt_server, strlen(srv) + 1);
     if (tmp == NULL) {
+        // keep the old value.  realloc leaves it valid on failure, and dropping it
+        // would hand every later reader a NULL
         PrintAndLogEx(WARNING, "Failed to allocate memory");
-        free(g_session.mqtt_server);
-        g_session.mqtt_server = NULL;
         return false;
     }
     g_session.mqtt_server = tmp;
@@ -84,9 +84,9 @@ static bool setDefaultMqttPort(const char *port) {
 
     char *tmp = (char *)realloc(g_session.mqtt_port, strlen(port) + 1);
     if (tmp == NULL) {
+        // keep the old value.  realloc leaves it valid on failure, and dropping it
+        // would hand every later reader a NULL
         PrintAndLogEx(WARNING, "Failed to allocate memory");
-        free(g_session.mqtt_port);
-        g_session.mqtt_port = NULL;
         return false;
     }
     g_session.mqtt_port = tmp;
@@ -107,9 +107,9 @@ static bool setDefaultMqttTopic(const char *topic) {
 
     char *tmp = (char *)realloc(g_session.mqtt_topic, strlen(topic) + 1);
     if (tmp == NULL) {
+        // keep the old value.  realloc leaves it valid on failure, and dropping it
+        // would hand every later reader a NULL
         PrintAndLogEx(WARNING, "Failed to allocate memory");
-        free(g_session.mqtt_topic);
-        g_session.mqtt_topic = NULL;
         return false;
     }
     g_session.mqtt_topic = tmp;