diff --git a/src/unixdef.h b/src/unixdef.h
new file mode 100644
index 0000000..3bfa67f
--- /dev/null
+++ b/src/unixdef.h
@@ -0,0 +1,26 @@
+#ifndef UNIXDEF_H
+#define UNIXDEF_H
+/*=========================================================================*\
+* Unix domain defines
+* LuaSocket toolkit
+*
+* Provides sockaddr_un on Windows and Unix.
+\*=========================================================================*/
+
+#ifdef _WIN32
+/* Technically it's possible to include <afunix.h> but it's only available
+   on Windows SDK 17134 (Windows 10 1803). */
+#ifndef AF_UNIX
+#define AF_UNIX 1
+#endif
+
+struct sockaddr_un
+{
+    unsigned short sun_family;
+    char sun_path[108];
+};
+#else
+#include <sys/un.h>
+#endif /* _WIN32 */
+
+#endif /* UNIXDEF_H */