https://bugs.gentoo.org/836572
--- a/tests/regression/client/client.c
+++ b/tests/regression/client/client.c
@@ -26,6 +26,7 @@
 #include <stdlib.h>
 #include <syscall.h>
 #include <sys/epoll.h>
+#include <sys/socket.h>
 #include <sys/types.h>
 #include <sys/un.h>
 #include <unistd.h>