diff --git a/src/oatpp-websocket/AsyncWebSocket.cpp b/src/oatpp-websocket/AsyncWebSocket.cpp
index 7b321b6..c5ecfeb 100644
--- a/src/oatpp-websocket/AsyncWebSocket.cpp
+++ b/src/oatpp-websocket/AsyncWebSocket.cpp
@@ -27,7 +27,7 @@
 #include "./Utils.hpp"
 
 #if defined(WIN32) || defined(_WIN32)
-  #include <WinSock2.h>
+  #include <winsock2.h>
 #else
   #include <arpa/inet.h>
 #endif
diff --git a/src/oatpp-websocket/SHA1.cpp b/src/oatpp-websocket/SHA1.cpp
index 057592e..9704e38 100644
--- a/src/oatpp-websocket/SHA1.cpp
+++ b/src/oatpp-websocket/SHA1.cpp
@@ -27,7 +27,7 @@
 #include <fstream>
 
 #if defined(WIN32) || defined(_WIN32)
-  #include <WinSock2.h>
+  #include <winsock2.h>
 #else
   #include <arpa/inet.h>
 #endif
diff --git a/src/oatpp-websocket/WebSocket.cpp b/src/oatpp-websocket/WebSocket.cpp
index 2d0ebd3..0235684 100644
--- a/src/oatpp-websocket/WebSocket.cpp
+++ b/src/oatpp-websocket/WebSocket.cpp
@@ -27,7 +27,7 @@
 #include "./Utils.hpp"
 
 #if defined(WIN32) || defined(_WIN32)
-  #include <WinSock2.h>
+  #include <winsock2.h>
 #else
   #include <arpa/inet.h>
 #endif