diff --git a/mrbgems/mruby-socket/src/socket.c b/mrbgems/mruby-socket/src/socket.c
index 4832a5b4e..7d9bfe99f 100644
--- a/mrbgems/mruby-socket/src/socket.c
+++ b/mrbgems/mruby-socket/src/socket.c
@@ -12,6 +12,7 @@
   #include <windows.h>
 
   #define SHUT_RDWR SD_BOTH
+  typedef int ssize_t;
 #else
   #include <sys/types.h>
   #include <sys/socket.h>