diff --git a/main/wifi_transport.c b/main/wifi_transport.c
index 2df1eb0..579524e 100644
--- a/main/wifi_transport.c
+++ b/main/wifi_transport.c
@@ -5,6 +5,7 @@
 #include "freertos/FreeRTOS.h"
 #include "freertos/task.h"
 #include "freertos/queue.h"
+#include "freertos/semphr.h"
 #include "esp_wifi.h"
 #include "esp_wifi_ap_get_sta_list.h"
 #include "esp_netif.h"
@@ -31,13 +32,18 @@ static struct {
 } clients[UDP_CLIENTS_MAX];
 
 static int client_count;
+static SemaphoreHandle_t client_mutex;
 
 static void client_touch(const struct sockaddr_in *addr)
 {
+    xSemaphoreTake(client_mutex, portMAX_DELAY);
+
     for (int i = 0; i < client_count; i++) {
         if (clients[i].addr.sin_addr.s_addr == addr->sin_addr.s_addr &&
-            clients[i].addr.sin_port == addr->sin_port)
+            clients[i].addr.sin_port == addr->sin_port) {
+            xSemaphoreGive(client_mutex);
             return;
+        }
     }
 
     if (client_count < UDP_CLIENTS_MAX) {
@@ -60,10 +66,13 @@ static void client_touch(const struct sockaddr_in *addr)
         client_count++;
         printf("UDP: client added (%d)\n", client_count);
     }
+
+    xSemaphoreGive(client_mutex);
 }
 
 static void client_remove_by_mac(const uint8_t *mac)
 {
+    xSemaphoreTake(client_mutex, portMAX_DELAY);
     for (int i = 0; i < client_count; ) {
         if (memcmp(clients[i].mac, mac, 6) == 0) {
             clients[i] = clients[--client_count];
@@ -72,6 +81,7 @@ static void client_remove_by_mac(const uint8_t *mac)
             i++;
         }
     }
+    xSemaphoreGive(client_mutex);
 }
 
 static void parse_udp_sysex(const uint8_t *data, uint16_t len)
@@ -221,6 +231,7 @@ int wifi_send_sysex(const uint8_t *sysex, uint16_t len)
     if (udp_sock < 0 || client_count == 0)
         return -1;
 
+    xSemaphoreTake(client_mutex, portMAX_DELAY);
     int sent = 0;
     for (int i = 0; i < client_count; i++) {
         int r = sendto(udp_sock, sysex, len, 0,
@@ -228,6 +239,7 @@ int wifi_send_sysex(const uint8_t *sysex, uint16_t len)
                        sizeof(clients[i].addr));
         if (r > 0) sent++;
     }
+    xSemaphoreGive(client_mutex);
     return sent > 0 ? 0 : -1;
 }
 
@@ -347,6 +359,8 @@ static int udp_init(void)
 
 int wifi_transport_init(void)
 {
+    client_mutex = xSemaphoreCreateMutex();
+
     int rc = wifi_ap_init();
     if (rc) {
         printf("WiFi: AP init failed: %d\n", rc);