diff --git a/src/modules/ESP8266/ESP8266.cpp b/src/modules/ESP8266/ESP8266.cpp
index c07a96e8..98d8c8d5 100644
--- a/src/modules/ESP8266/ESP8266.cpp
+++ b/src/modules/ESP8266/ESP8266.cpp
@@ -160,10 +160,10 @@ int16_t ESP8266::send(const char* data) {
   return(ERR_NONE);
 }
 
-int16_t ESP8266::send(uint8_t* data, uint32_t len) {
+int16_t ESP8266::send(uint8_t* data, size_t len) {
   // build AT command
   char lenStr[8];
-  sprintf(lenStr, "%lu", len);
+  sprintf(lenStr, "%u", (uint16_t)len);
   const char atStr[] = "AT+CIPSEND=";
   #ifdef RADIOLIB_STATIC_ONLY
     char cmd[RADIOLIB_STATIC_ARRAY_SIZE];
diff --git a/src/modules/ESP8266/ESP8266.h b/src/modules/ESP8266/ESP8266.h
index eff7b8b0..cc999500 100644
--- a/src/modules/ESP8266/ESP8266.h
+++ b/src/modules/ESP8266/ESP8266.h
@@ -51,7 +51,7 @@ class ESP8266: public TransportLayer {
     int16_t openTransportConnection(const char* host, const char* protocol, uint16_t port, uint16_t tcpKeepAlive = 0) override;
     int16_t closeTransportConnection() override;
     int16_t send(const char* data) override;
-    int16_t send(uint8_t* data, uint32_t len) override;
+    int16_t send(uint8_t* data, size_t len) override;
     size_t receive(uint8_t* data, size_t len, uint32_t timeout = 10000) override;
     size_t getNumBytes(uint32_t timeout = 10000, size_t minBytes = 10) override;