+AC_CHECK_HEADERS([netinet/in.h], [], [], [dnl
+#include <stdio.h>
+#ifdef STDC_HEADERS
+# include <stdlib.h>
+# include <stddef.h>
+#else
+# ifdef HAVE_STDLIB_H
+# include <stdlib.h>
+# endif
+#endif
+#ifdef HAVE_SYS_SOCKET_H
+# include <sys/socket.h>
+#endif
+])
+AC_CHECK_HEADERS(netinet/tcp.h, [], [], [dnl
+#include <stdio.h>
+#ifdef STDC_HEADERS
+# include <stdlib.h>
+# include <stddef.h>
+#else
+# ifdef HAVE_STDLIB_H
+# include <stdlib.h>
+# endif
+#endif
+#ifdef HAVE_SYS_SOCKET_H
+# include <sys/socket.h>
+#endif
+])