diff --git a/src/io.h b/src/io.h
index d380f34a..9b5305db 100644
--- a/src/io.h
+++ b/src/io.h
@@ -13,6 +13,7 @@
 
 #ifndef WIN32
 # include <netinet/in.h>
+# include <sys/socket.h>
 #else
 #define WIN32_LEAN_AND_MEAN
 # include <windows.h>