diff --git a/examples/protocols/asio/chat_client/main/chat_client.cpp b/examples/protocols/asio/chat_client/main/chat_client.cpp
index d4a111057..0b0f7097f 100644
--- a/examples/protocols/asio/chat_client/main/chat_client.cpp
+++ b/examples/protocols/asio/chat_client/main/chat_client.cpp
@@ -134,7 +134,7 @@ private:
 void read_line(char * line, int max_chars);
 
 
-extern "C" void app_main()
+extern "C" void app_main(void)
 {
     ESP_ERROR_CHECK(nvs_flash_init());
     tcpip_adapter_init();
diff --git a/examples/protocols/asio/chat_server/main/chat_server.cpp b/examples/protocols/asio/chat_server/main/chat_server.cpp
index 56a447e05..c1838b53f 100644
--- a/examples/protocols/asio/chat_server/main/chat_server.cpp
+++ b/examples/protocols/asio/chat_server/main/chat_server.cpp
@@ -202,7 +202,7 @@ private:
 
 //----------------------------------------------------------------------
 
-extern "C" void app_main()
+extern "C" void app_main(void)
 {
     ESP_ERROR_CHECK(nvs_flash_init());
     tcpip_adapter_init();
diff --git a/examples/protocols/asio/tcp_echo_server/main/echo_server.cpp b/examples/protocols/asio/tcp_echo_server/main/echo_server.cpp
index 008ec6ed7..d1ed69e05 100644
--- a/examples/protocols/asio/tcp_echo_server/main/echo_server.cpp
+++ b/examples/protocols/asio/tcp_echo_server/main/echo_server.cpp
@@ -84,7 +84,7 @@ private:
 };
 
 
-extern "C" void app_main()
+extern "C" void app_main(void)
 {
     ESP_ERROR_CHECK(nvs_flash_init());
     tcpip_adapter_init();
diff --git a/examples/protocols/asio/udp_echo_server/main/udp_echo_server.cpp b/examples/protocols/asio/udp_echo_server/main/udp_echo_server.cpp
index 06ac3fec9..68adf4148 100644
--- a/examples/protocols/asio/udp_echo_server/main/udp_echo_server.cpp
+++ b/examples/protocols/asio/udp_echo_server/main/udp_echo_server.cpp
@@ -66,7 +66,7 @@ private:
   char data_[max_length];
 };
 
-extern "C" void app_main()
+extern "C" void app_main(void)
 {
     ESP_ERROR_CHECK(nvs_flash_init());
     tcpip_adapter_init();